craig, i tink yule like yer bi-amped set-up, but as yuve also had yer amps seriously upgraded, i imagine lotsa improvement wood be evident even if using only *one* amp in a bi-wire mode.
supakit, whether or not 4 channel for passive bi-amping is better than bridging & having 2-channel w/bi-wiring, depends, in part on the power-requirements of your speakers. if, for example, yer bass driver/s really need 200w to come alive, & yer 4-channel amp is, say, 100wpc, then bridging the amps to two-channel, w/anywhere from 200-400wpc, will prolly be better. but, if each channel of yer four-channel amp is more than enuff power for the load it'll see in a bi-amped configuration, it will prolly sound better when run bi-amped.
hope this helps, doug s.