Tesla S1070 for Dell R815

I just got a new Dell R815 server (4x Opteron 6174s) running RHEL 5.6 and want to attach half of my Tesla S1070 to it. I took one of the two host interface cards from the other computer that the S1070 is connected to and put it in the R815, and connected the cable from the S1070 to the R815. The R815 does not recognize the two GPUs that are connected to it. /sbin/lspci shows the adapter card but not the GPUs:

23:00.0 PCI bridge: nVidia Corporation NF200 PCIe2.0 switch for Quadro Plex S4 / Tesla S870 / Tesla S1070 / Tesla S2050 (rev a2)
24:00.0 PCI bridge: nVidia Corporation NF200 PCIe2.0 switch for Quadro Plex S4 / Tesla S870 / Tesla S1070 / Tesla S2050 (rev a2)
24:01.0 PCI bridge: nVidia Corporation NF200 PCIe2.0 switch for Quadro Plex S4 / Tesla S870 / Tesla S1070 / Tesla S2050 (rev a2)
24:02.0 PCI bridge: nVidia Corporation NF200 PCIe2.0 switch for Quadro Plex S4 / Tesla S870 / Tesla S1070 / Tesla S2050 (rev a2)
24:03.0 PCI bridge: nVidia Corporation NF200 PCIe2.0 switch for Quadro Plex S4 / Tesla S870 / Tesla S1070 / Tesla S2050 (rev a2)

The other computer shows ten instances of the PCI bridge and two 3D controllers from nVidia.

Is the problem:
(a) a BIOS problem with the R815 (i.e. call Dell);
(b) the R815 has x16 PCIe v2.0 physical slots but only x8 electrical slots;
© something else entirely?

Nvidia lists the S1070 as having been tested with the R410, R610, R710 and R900.

Hell e.ping
I know it’s been 6 years now. I am having similar problem with r710. S1070 is not even power on. This is first time I am using this S1070. I have only r710 and I connected both HCI cables to r710 (other end to s1070).
I see 10 bridges detected on r710. But no GPUs. S1070 is not even power on. I can feel s1070 psu getting little hot (so power is getting in but it’s waiting for power signal from host). I am not sure what to do next.
Is your problem solved?