I am in the process of upgrading my system and am either going with on Outlaw 7500 or 7700. I will be using my Onkyo TX-NR900 as a pre/pro for the moment. I'd like to bi-amp the RTi12's using 4 of the amp channels. With the 7500 I'd use the last channel for the CSi5 and then let the AVR run my two FXi3's. With the 7700 all speakers would be run off of the amp leaving the AVR purely as a pre/pro.
My concern with the 7500 is that the FXi3's will be significantly underpowered even though only about 15% of the sound typically comes from them in HT.