If you set up a wave maker correctly, you don't need that much power to form a standing wave, in my 30 gal long tank, a RW4 is enough to form a standing wave about 1/4" high, when set up length wise. (an RW 8 would be better here if I want to get it to 1/2" high for better water movement)
In my standard 65 gal, tank, the RW8 will create a 3/8" high standing wave (at max output of 2000 gal/hr), when I have the pump on the back corner blowing forward or on the side, set up length wise. I've stopped using this feature since my tank was rocking 1mm front to back with every wave when placed on the back. I didn't want to place the pump on the side, though that was working fine.
I have since gone with 2 RW8s but am not using the wave making function, because though they are suppose to sync and pulse water together, the wireless feature causes it to miss some signals causing the waves to clash with each other and neutralize more often then not, therefore preventing me from setting up my perfectly flowing system.
SO for your 93 cube, I would go with one RW15, placed center back and set it around 2000 to 2500 gal/hr speed (well below the top output, but around the output of the RW8) and create a standing wave no greater than 3/8" high. I believe the RW15 can create waves a few inches high, but that will strain your stand. If the RWs can communicate effectively with each other, I would go with 2 RW8s, but my experience says go with a single pump since they do not. (I have placed the 2 controls right next to each other to try and drop as little signals as possible, but there is a flaw here. When the pumps first start in the morning and go from night cycle to day cycle, there is a 50/50 chance that they either both blow at the same time, or alternate)