First of all, the 935 is getting hard to get a hold of so good luck. It does come with a cover for the empty PSU slot and also a black chrome motherboard backplate for the 915 section. If you plan on using an extra large PSU you will have to fit it into the 915 section. There are 8 expansion slots on the 925 section. You could look into the CM Trooper or Stryker case that has 9 expansion slots. The reason why most gaming builds only have 1 or 2 graphics cards is frame pacing or the cost/performance gain ratio I suppose. Frame pacing is an issue with multi GPU setups especially on 3 and 4 card setups. New Catalyst drivers are designed to where an AMD APU can improve this some. I would recommend using an AMD processor with AMD GPUs or an Intel processor with Nvidia GPUs anyway. There is a 1500 watt version of the CM Silent Pro M2 (80+ silver rating), but I believe the V1200 Platinum would handle a system with 3 R9 390Xs. The R9 390X is supposedly going to consume less than 300 watts by the way.