I use 2x DPS-1200 PSUs for my power hungry rigs. Without any problem.
Half of the GPUs on each PSU.
And I use picoATX, or a completely separate cheap ($15) ~400W ATX for the mobo+ssd.
The only potential problem is if the ATX turns on 1-2 seconds earlier than the DPS and the mobo powers up with no power on the GPUs yet so the cards won't get detected.
But I got a simple solution also for that. A little LC delay loop soldered to the green ATX wire, that gives a few second delay before the mobo turning on.