True bi-amping with external crossovers will net you some gain. Passive bi-amping using the crossovers in the speaker may gain you some headroom but not much of anything else. Everyone has a different opinion on this and there are a thousand threads about it on here. Just do a search and you will find them.
You need an amp or AVR that is 4ohm stable. Some AVRs are 4ohm stable, you could always start with a beefy AVR and the add an amp later if ther AVR will not truely power your speakers.
For an all out, true pre/pro, look at the Integra DTC 9.8 (~ $1600) and either use a pro amp or a HT amp as described in earlier post.
Like I said before, today's AVRs make awesome pre/pros and you can go that route too. Look at Pioneer Elites (the ICE amp models will likely be 4 ohm stable and may not need an amp) Denon and Yamaha.
Many forum members also like to use Emotiva amps. They are inexpensive and very powerful so you may want to add this to your list along with the Outlaw and Rotel.
