I can only help you with your first question. The potential disadvantage of biamping is totally messing up the decent sound you now enjoy. The differences in amplifier timing, slew rate and dynamics make biamping risky at best. If you do it, here's my opinion on the only way to do it right: Get two identical model amps - or as close as you can get - same model & serial numbers as close as possible. Then use what's called "Vertical Biamping." That is where you use one amp to drive the high & low frequency drivers of the same speaker - as opposed to "Horizontal Biamping" which is using one amp for the highs of both speakers and one for the lows. Vertical biamping has the possibilty of the least amount of timing error being introduced into the system. Timing errors introduce dynamic incompatabilities that are easily heard as a loss of total system dynamics. I have experimented with a number of setups using various equipment and have concluded that the average listener (a group in which I certainly count myself) is better off using a good quality amp, speakers, and cables and simply enjoying what you have. Remember KISS: Keep It Simple Stupid. It's as good a piece of advice in audio as it is in any other endeavor.
Hope this helps,
Ed
Hope this helps,
Ed