Not any good ones....is there any reason for not going with the larger RTi6?
Bi-amping w AVR= worthless.@Drumz : I didn't see anyone else address this, so I'll take a stab at it and one of the old-timers can correct me if I say anything too egregiously wrong...
All of the AVRs have the ability because even though it is useless, the manufacturers have to "keep up with the Joneses" and maintain feature parity within their price point. Bi-amping is just one more instance of the triumph of marketing nonsense over actual reality.
While bi-amping in theory might have some positive effect on the sound, it's really only possible to get that if you are literally running the two halves of the speaker from separate dedicated amps or a dedicated amp that has separate power supplies/transformers for each channel. Bi-amping from an AVR is useless because just about all AVRs are running all of their channels from one power supply, so power going to any one channel takes away from power available to the other channels, which defeats the whole purpose of having increased power "headroom" available to the upper and lower halves of your speaker when bi-amping. Speaking more practically, for the ears that most of us have anyway, even if you were to bi-amp the real way with dedicated amps with power to spare, the gains you may get don't really outweigh the expense you are now undertaking for extra amps.
Full disclosure: I've never used dedicated amps, and so do not have direct experience of any sound benefits to be gained from them, with or without bi-amping. Many folks on this forum use dedicated amps in their setups. I don't know who, if any, bi-amps with them.
More full disclosure: my RT800i fronts are bi-amped to my Yammie RX-A700 because at the time I built the system just about two years ago, 1) I knew I wasn't going to have rear surrounds for the foreseeable future and so would have 2 spare channels, and 2) I didn't know any better. Now it's just too much of a pain in the ass to pull everything out of the entertainment unit and undo it, so I leave it that way until I figure out how to put rear surrounds into my HT space.
Bi-amping with dedicated amps = worthless 99% of the time unless you've got REALLY GOOD gear (which my and your gear doesnt qualify as)
I've done bi-amping with a dedicated amp before and no difference even with my LSI 15's. The only real difference it makes is a bit more clarity at volumes so loud they are unrealistic. Been there done that, wasn't worth the work.
The only "real" benefits of bi-amping are when you go truly "active" by removing the crossover and connecting directly from the amp to speakers. Its normally not worth doing so dont even stress it.
Get the right amount of wattage on your speakers and it wont be something you worry about. Most folks suggest something in the 200 wpc @ 8 ohms for the RTi A line. I'd say Emotiva, Parasound, Carver, Outlaw, ATI are good brands to checkout. I'm not a huge Emo fan, but they are good for what they are. You could get a 2 or 3 channel amp for your fronts and that would be fine. The more speakers you take off your AVR the more wattage it can provide to what remains. Surrounds & Rear Surrounds are easy to drive so no need to amp them unless you just want to (which is ok).
Even just a really good 2 channel amp to handle your fronts would work as well, and if you like music would ensure when listening to stereo that you've got adequate power.
I had a Carver AV-705x on my LSi 5 channel for years, never felt it was lacking. That said the disease of upgraditius hit me and I bought a B&K 200.5 which is 375 wpc @ 4 ohms, and let me tell you my house is shaking when I turn it up.