Dual Invidia Q4000 Cards, but can only use 2 Monitors, why?

Hello,

I have a Dell T420, with Dual Procs, 384g ram, redundant 1100w power supplies.

I also have 2 Dell Invidia Quadro 4000 Video cards

Both are plugged into CPU 1 and 2 slots, and both have power from the power distribution/backplanes.

They are both recognized by Windows and have no issues.

However, I am only able to get 2 monitors to work. I thought I only needed 1 Q4000 to drive 3 monitors, but found out that 1 will only drive 2 monitors

So I bought a second card and put it in the machine. But I can use 1 DVI and 1 DP on card 1, but if I plug into card 2, I still only see 2 display outputs

No matter what cables and how I plug them in its only 2. If I plug in DVI + DP on either card, then use DP on the second card it doesn't matter.

Are dual Q4000 only good for SLI but still limited to 2 monitors?

Do I need to instead, turn off the onboard GPU and then I can use 3-4 monitors with the 2 cards?

Thanks!