The sonic benefits are that you bypass the crossover of the speaker which may be just a cheaply made filter and drive them separately.
Unfortunately, not quite. You need a crossover, whether it's in the speaker, or upstream of the power amps. Simply bi-amping a standard pair of speakers will NOT by-pass the crossover. To do the job with what you're suggesting, you'd need something like a Linn tunebox or Naim SNAXOS prior to the power amps.
As for the effects of bi-amping. In short, it'll give you more "grunt", kind of like doubling the torque of a car. That will improve bass control and reduce distortion. Having said that, it won't be an improvement to the basic circuits, as all you're doing is duplicating them.
The implications are that for the cost of bi-amping, you might well be better off with a single amp that cost twice the amount and has a better layout and higher quality components.
In the real world, it's dependent upon the system with which it's being used. I've seen reports both ways about the cost effectiveness of bi-amping.
If I were to look at bi-amping, I think I'd go the whole hog and go active, but in that case I'd probably look at something like the ATC range of active speakers. They not only have separate amps, but also have their amps "tuned" to work with the drivers.
Let me put it like this, I heard a pair of active ATCs recently, and IMO they were some of the best speakers I've ever heard, although they still don't have the attack that a good pair of horns give.
