The answer to 1 depends on how you are bi-amping. If you have an active crossover in front of the amps to divide up the frequency spectrum, bi-amping is always better if you have enough power (but you need less that not bi-amping). If you are going to amplify the entire spectrum and have the internal crossovers divide it up, the answer is probably indeterminate. It will vary based on what you are listening to (i.e., from disk to disk). What will happen is that you will share power from channel to channel within the same amp, but you are still wasting power by amplifying the entire spectrum to use only a part of it. This is offset by typically not having enough power, but you could with the 806 just go bridged and get 360 without bi-amping.
That said, bridging does affect the sound, IMHO. Bridging the bass isn't as bad as bridging the treble. I think what makes bridging sound bad to me is just slight timing differences as the signal goes through all those components on both channels and are combined back together. It's like jitter. There seems to me to be a little smearing that you won't notice in the bass as much.
So, you do have a choice. But the answer to 2 is yes, depending on your definition of "significant".
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