I really and truly wish that I could do 6 IB's. Unfortunately that just isn't the case. If I do decide to go with the two 18's and I'm getting the impression that it is a feasible option. I'm thinking of using DIYsoundgroup speakers for the rest of the system. If I pair up 4 of the Fusion-6's for surround duties, and 2 Fusion-10 Pures for LR and a Fusion-4 Quad4 for Center, would there be any large holes in the system? I have wiring in place for the 6's to hang from ceiling.