CyberCrist, I was able to get 6 EVGA 750Ti FTW cards running on the ASRock Z87 Killer.
PCI-E 1 (gen2)
PCI-E 2 (gen1)
PCI-E 3 (gen1)
Also disabled integrated graphics and changed PEG0 De-emphasis Control to -6dB
PCI-E 1 (x1) --> 750 TI (1x riser, shorted)
PCI-E 2 (x16) --> 750 TI (1x riser, shorted)
PCI-E 3 (x1) --> 750 TI (1x riser, shorted)
PCI-E 4 (x1) --> 750 TI (1x riser, shorted)
PCI-E 5 (x16) --> 750 TI (1x USB riser, shorted)
PCI-E 6 (x1) --> 750 TI (1x riser, shorted)
PCI-E 7 (x16) --> EMPTY
It's messy at the moment and I have to clean up now that it's working but here are pics for proof. It's funny, we're very close in the equipment we used
I tried using a bootable Linux USB stick but had issues so I'm using an old hard drive. I have an EVGA 750W PSU but it's only pulling about 460W from the wall. These cards run very cool. I don't have a 7th card to try and I likely won't. For some reason I couldn't get a ribbon riser (also shorted) to work in the PCI-E 5 (x16) slot and when I tried a USB riser, it worked. I have a monitor plugged into the PCI-E 2 (x16) slot. Just like you I don't want to mess with it now that it works.
I am upset that I can't overclock these cards in Linux. There's so much more potential. What speeds are you getting with all 6? I am getting about 1550 KH/s mining Litecoin with CudaMiner.