How to configure a 3-card system?

I have a 3-yr old desktop running Ubuntu. It has two nvidia cards - a Quadro NVS 285 connecting to my dual-monitors, and a GTX 590 for dedicated GPU computing with CUDA. It has been working fine over the past few years.

I just bought a GTX 980 Ti and plan to use it along-side with my 590 for computing. Because my MOBO (MSI P67A-GD65) has only two PCIe 16x slots, so I bought a GTX 730 low-profile card with PCIe 1x interface to replace the Quadro 285 for display. So, the GTX 980Ti and 590 will occupy the 1st and 2nd PCIe x16 slots, and the 730 will go to the first PCIe x1 slot.

The problem I have right now is that the 730 does not give me any video output when connected to a monitor. In fact, only the card in the first (primary) PCIe x16 slot can output video signals. I can not use any other slot to drive my monitors unless I remove all cards but one.

I called MSI CS, wan’t very helpful, only did a bios update, but nothing changed.

Has anyone configured a multiple GPU system, particularly with a mix of PCI x16 and lower speed slots? did you make any changes in the bios?