Base Mosaic, unable to make it work...

Running :
Linux mint 17.3
Kernel 3.19.0-32-generic
Graphic cards : 2x GeForce GTX550
driver : 352.63
Computer : HP Z420

Hello I have an issue configuring base mosaic on my system.

The final configuration I’m targeting is to run 6 screens on two GTX 970 (same environment)
The thing is that there are in a production environment and I don’t want to brick the installation with hazardous commands for now :-).
FYI I get the exact same output on both computer.

For now I’m just trying to get my two GTX550 to work.

Here is my xorg :

# nvidia-xconfig: X configuration file generated by nvidia-xconfig
# nvidia-xconfig:  version 352.63  (buildmeister@swio-display-x64-rhel04-11)  Sat Nov  7 22:00:19 PST 2015

# nvidia-settings: X configuration file generated by nvidia-settings
# nvidia-settings:  version 352.39  (buildmeister@vm-ubuntu1404-x64-001)  Fri Aug 14 21:52:24 PDT 2015

Section "ServerLayout"
    Identifier     "Layout0"
    Screen      0  "Screen0" 0 0
    InputDevice    "Keyboard0" "CoreKeyboard"
    InputDevice    "Mouse0" "CorePointer"
    Option         "Xinerama" "0"
EndSection

Section "Files"
EndSection

Section "InputDevice"

    # generated from default
    Identifier     "Mouse0"
    Driver         "mouse"
    Option         "Protocol" "auto"
    Option         "Device" "/dev/psaux"
    Option         "Emulate3Buttons" "no"
    Option         "ZAxisMapping" "4 5"
EndSection

Section "InputDevice"

    # generated from default
    Identifier     "Keyboard0"
    Driver         "kbd"
EndSection

Section "Monitor"

    # HorizSync source: edid, VertRefresh source: edid
    Identifier     "Monitor0"
    VendorName     "Unknown"
    ModelName      "HP ZR2440w"
    HorizSync       24.0 - 80.0
    VertRefresh     24.0 - 60.0
    Option         "DPMS"
EndSection

Section "Device"
    Identifier     "Device0"
    Driver         "nvidia"
    VendorName     "NVIDIA Corporation"
    BoardName      "GeForce GTX 550 Ti"
EndSection

Section "Screen"
    Identifier     "Screen0"
    Device         "Device0"
    Monitor        "Monitor0"
    DefaultDepth    24
    Option         "Stereo" "0"
    Option         "nvidiaXineramaInfoOrder" "DFP-1"
    Option         "metamodes" "GPU-a6ea68d3-096c-ebba-14be-90eace404143.HDMI-0: 1920x1200_60 +0+0, GPU-cc4e6736-cfa4-f8b5-a505-8da3a5b0039d.DVI-I-3: 1920x1200_60 +1920+0"
    Option         "MultiGPU" "Off"
    Option         "SLI" "off"
    Option         "BaseMosaic" "True"
    SubSection     "Display"
        Depth       24
    EndSubSection
EndSection

And the startx output

[  1332.079] 
X.Org X Server 1.17.1
Release Date: 2015-02-10
[  1332.079] X Protocol Version 11, Revision 0
[  1332.079] Build Operating System: Linux 3.19.0-28-generic x86_64 Ubuntu
[  1332.079] Current Operating System: Linux tartarus 3.19.0-32-generic #37~14.04.1-Ubuntu SMP Thu Oct 22 09:41:40 UTC 2015 x86_64
[  1332.079] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-3.19.0-32-generic root=UUID=13b45c94-c9e0-40bc-9a20-634009e6802d ro quiet splash iommu=pt iommu=1
[  1332.080] Build Date: 11 September 2015  10:33:14AM
[  1332.080] xorg-server 2:1.17.1-0ubuntu3.1~trusty1 (For technical support please see http://www.ubuntu.com/support) 
[  1332.080] Current version of pixman: 0.30.2
[  1332.080] 	Before reporting problems, check http://wiki.x.org
	to make sure that you have the latest version.
[  1332.080] Markers: (--) probed, (**) from config file, (==) default setting,
	(++) from command line, (!!) notice, (II) informational,
	(WW) warning, (EE) error, (NI) not implemented, (??) unknown.
[  1332.081] (==) Log file: "/var/log/Xorg.0.log", Time: Fri Apr 22 18:41:35 2016
[  1332.082] (==) Using config file: "/etc/X11/xorg.conf"
[  1332.082] (==) Using system config directory "/usr/share/X11/xorg.conf.d"
[  1332.082] (==) ServerLayout "Layout0"
[  1332.082] (**) |-->Screen "Screen0" (0)
[  1332.082] (**) |   |-->Monitor "Monitor0"
[  1332.083] (**) |   |-->Device "Device0"
[  1332.083] (**) |-->Input Device "Keyboard0"
[  1332.083] (**) |-->Input Device "Mouse0"
[  1332.083] (**) Option "Xinerama" "0"
[  1332.083] (==) Automatically adding devices
[  1332.083] (==) Automatically enabling devices
[  1332.083] (==) Automatically adding GPU devices
[  1332.083] (WW) The directory "/usr/share/fonts/X11/cyrillic" does not exist.
[  1332.083] 	Entry deleted from font path.
[  1332.083] (WW) The directory "/usr/share/fonts/X11/100dpi/" does not exist.
[  1332.083] 	Entry deleted from font path.
[  1332.083] (WW) The directory "/usr/share/fonts/X11/75dpi/" does not exist.
[  1332.083] 	Entry deleted from font path.
[  1332.083] (WW) The directory "/usr/share/fonts/X11/100dpi" does not exist.
[  1332.083] 	Entry deleted from font path.
[  1332.083] (WW) The directory "/usr/share/fonts/X11/75dpi" does not exist.
[  1332.083] 	Entry deleted from font path.
[  1332.083] (==) FontPath set to:
	/usr/share/fonts/X11/misc,
	/usr/share/fonts/X11/Type1,
	built-ins
[  1332.083] (==) ModulePath set to "/usr/lib/x86_64-linux-gnu/xorg/extra-modules,/usr/lib/xorg/extra-modules,/usr/lib/xorg/modules"
[  1332.083] (WW) Hotplugging is on, devices using drivers 'kbd', 'mouse' or 'vmmouse' will be disabled.
[  1332.083] (WW) Disabling Keyboard0
[  1332.083] (WW) Disabling Mouse0
[  1332.083] (II) Loader magic: 0x7fe7cffd2c60
[  1332.083] (II) Module ABI versions:
[  1332.083] 	X.Org ANSI C Emulation: 0.4
[  1332.083] 	X.Org Video Driver: 19.0
[  1332.083] 	X.Org XInput driver : 21.0
[  1332.083] 	X.Org Server Extension : 9.0
[  1332.083] (II) xfree86: Adding drm device (/dev/dri/card0)
[  1332.083] (II) xfree86: Adding drm device (/dev/dri/card1)
[  1332.088] (--) PCI: (0:3:0:0) 10de:1244:3842:1557 rev 161, Mem @ 0xcc000000/33554432, 0xe0000000/134217728, 0xe8000000/67108864, I/O @ 0x0000d000/128, BIOS @ 0x????????/524288
[  1332.088] (--) PCI:*(0:5:0:0) 10de:1244:3842:1557 rev 161, Mem @ 0xc8000000/33554432, 0xd0000000/134217728, 0xd8000000/67108864, I/O @ 0x0000c000/128, BIOS @ 0x????????/524288
[  1332.088] (WW) "glamoregl" will not be loaded unless you've specified it to be loaded elsewhere.
[  1332.088] (II) "glx" will be loaded by default.
[  1332.088] (II) LoadModule: "glx"
[  1332.088] (II) Loading /usr/lib/x86_64-linux-gnu/xorg/extra-modules/libglx.so
[  1332.103] (II) Module glx: vendor="NVIDIA Corporation"
[  1332.103] 	compiled for 4.0.2, module version = 1.0.0
[  1332.103] 	Module class: X.Org Server Extension
[  1332.103] (II) NVIDIA GLX Module  352.63  Sat Nov  7 20:52:00 PST 2015
[  1332.103] (II) LoadModule: "nvidia"
[  1332.103] (II) Loading /usr/lib/x86_64-linux-gnu/xorg/extra-modules/nvidia_drv.so
[  1332.103] (II) Module nvidia: vendor="NVIDIA Corporation"
[  1332.104] 	compiled for 4.0.2, module version = 1.0.0
[  1332.104] 	Module class: X.Org Video Driver
[  1332.104] (II) NVIDIA dlloader X Driver  352.63  Sat Nov  7 20:29:25 PST 2015
[  1332.104] (II) NVIDIA Unified Driver for all Supported NVIDIA GPUs
[  1332.104] (--) using VT number 7

[  1332.106] (II) Loading sub module "fb"
[  1332.106] (II) LoadModule: "fb"
[  1332.107] (II) Loading /usr/lib/xorg/modules/libfb.so
[  1332.107] (II) Module fb: vendor="X.Org Foundation"
[  1332.107] 	compiled for 1.17.1, module version = 1.0.0
[  1332.107] 	ABI class: X.Org ANSI C Emulation, version 0.4
[  1332.107] (II) Loading sub module "wfb"
[  1332.107] (II) LoadModule: "wfb"
[  1332.107] (II) Loading /usr/lib/xorg/modules/libwfb.so
[  1332.107] (II) Module wfb: vendor="X.Org Foundation"
[  1332.107] 	compiled for 1.17.1, module version = 1.0.0
[  1332.107] 	ABI class: X.Org ANSI C Emulation, version 0.4
[  1332.107] (II) Loading sub module "ramdac"
[  1332.107] (II) LoadModule: "ramdac"
[  1332.107] (II) Module "ramdac" already built-in
[  1332.108] (**) NVIDIA(0): Depth 24, (--) framebuffer bpp 32
[  1332.108] (==) NVIDIA(0): RGB weight 888
[  1332.108] (==) NVIDIA(0): Default visual is TrueColor
[  1332.108] (==) NVIDIA(0): Using gamma correction (1.0, 1.0, 1.0)
[  1332.108] (**) NVIDIA(0): Option "Stereo" "0"
[  1332.108] (**) NVIDIA(0): Option "nvidiaXineramaInfoOrder" "DFP-1"
[  1332.108] (**) NVIDIA(0): Option "SLI" "off"
[  1332.108] (**) NVIDIA(0): Option "MultiGPU" "Off"
[  1332.108] (**) NVIDIA(0): Option "BaseMosaic" "True"
[  1332.108] (**) NVIDIA(0): Stereo disabled by request
[  1332.108] (**) NVIDIA(0): NVIDIA SLI disabled.
[  1332.108] (**) NVIDIA(0): NVIDIA Multi-GPU disabled.
[  1332.108] (**) NVIDIA(0): Option "MetaModes" "GPU-a6ea68d3-096c-ebba-14be-90eace404143.HDMI-0: 1920x1200_60 +0+0, GPU-cc4e6736-cfa4-f8b5-a505-8da3a5b0039d.DVI-I-3: 1920x1200_60 +1920+0"
[  1332.108] (**) NVIDIA(0): Enabling 2D acceleration
[  1332.563] (EE) NVIDIA(GPU-0): Failed to find a valid Base Mosaic configuration.
[  1332.563] (EE) NVIDIA(GPU-0): Invalid Base Mosaic configuration 1 of 1:
[  1332.563] (EE) NVIDIA(GPU-0): GPUs:
[  1332.563] (EE) NVIDIA(GPU-0):     1) NVIDIA GPU at PCI:3:0:0
[  1332.563] (EE) NVIDIA(GPU-0):     2) NVIDIA GPU at PCI:5:0:0
[  1332.563] (EE) NVIDIA(GPU-0): Errors:
[  1332.563] (EE) NVIDIA(GPU-0):     - The video link was not detected
[  1332.563] (EE) NVIDIA(GPU-0):     - Unknown error
[  1332.563] (WW) NVIDIA(GPU-0): Failed to find a valid Base Mosaic configuration for the
[  1332.563] (WW) NVIDIA(GPU-0):     NVIDIA graphics device PCI:5:0:0. Please see Chapter 28:
[  1332.563] (WW) NVIDIA(GPU-0):     Configuring SLI and Multi-GPU FrameRendering in the README
[  1332.563] (WW) NVIDIA(GPU-0):     for troubleshooting suggestions.

As described on your website I already tried to disable NvidiaXineramaInfo and Compositing

Any way to get more information and solve this issue ?

Regards