Hello Spencer,
Sorry I couldn't resist giving you a hard time
Coming from car audio you are probably accustomed to big amplification and tiny sealed boxes. The Tiny sealed box essentially acts as a damper on efficiency, resulting in the need for enormous amplification power to overcome. When woofers are loaded in large reflex enclosures, they maintain their sensitivity down to much lower frequencies. The result is that, they will generally run out of Xmax long before they run out of thermal power handling. I think you may be surprised to see how dramatic the effects are. Xmax limited power handling at 1/10th the thermal rating is not terribly uncommon.
Having plenty of clean power is always desirable, however, there is nothing inherently wrong with using a 10W amp to power a 1000W rated speaker, nor is there anything inherently wrong with using a 1000W amp to power a 10W rated speaker. It really boils down to what it is that the system is trying to accomplish and personal tastes.
The primary advantage to bi-amping, IMO, is the elimination of complex passive crossovers. Active x-overs are not effected by the massive variations in driver impedance through the listening range, and do not introducing phase/timing issues. When you set up a bi-amped system, it's important that you select amplifiers with matching gain structure. Hopefully the receivers you are interested in include the necessary information to properly select an separate amp. Personally If I were that serious, I would not buy a "receiver" but rather, a surround processor/pre-amp and then a series of dedicated power amplifiers. Perhaps bi-amping the 3 front mains (each channel would need a stereo amp), then just using an additional pair of stereo amps to power the 4 "surround" channels (no bi-amping there). Keep in mind that some speakers will not benefit from bi-amping unless the x-over point is properly selected and adjusted (amount of overlap), and in some cases, EQed. With many speakers, the passive x-over is tailored to correct for various dips and rises in driver efficiency and is actually used to "fix" issues with the drivers and the way they mate up, if you by-pass that and go active x-over and bi-amped, you are effectively eliminating the x-over contours that solved those problems and inserting "generic" roll offs. I suggest picking out a system with a calibrated mic and -good- EQ so you can solve these problems.
A 15" driver is always going to be limited to *relatively* low frequency ranges simply because of it's diameter. Off axis response of a 15" driver probably starts to fade somewhere in the 500-1000hz range (not sure exactly), and a 15" driver will (unless carefully dampened) have an on-axis peak that is pretty nasty around 1000-1500hz. The use of a 15" driver above ~500-1000hz gets tricky, through many implementations do use them up to 1K and well beyond, some more successfully than others (well designed/dampened 15" drivers in on-axis applications can be used to ~2-3K pretty effectively). As far as large drivers go that can sound good. Pro audio drivers from JBL, B&C, and RCF generally come very highly regarded and are commonly used in studio reference applications ( I'll take 2 of these when I win the lotto:
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=294-689 ). Though there are many well regarded pro drivers from less pricey brands that can deliver startlingly hair raising impact and accuracy.
I haven't heard cerwin vega horns so really can't comment (or if I have heard them, I don't recall). Decent compression drivers seem to start around $40-50, many popular models in that price range from Selenium are popular in the DIY community. Like anything in this world, you can always throw more money at the problem (
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=294-410 )... If you've ever heard a really high end JBL sound reinforcement rig then you'd get a chance to hear a large format driver and horn that sound every bit as non-fatiguing or better than most high end "hifi" stuff.
Regards,
Eric