The main advantage of using mono blocks over stereo amps is that typically, stereo amps use components, chasis, cords, etc. that are shared between channels. With this you get crosstalk. Also, and more importantly, a stereo amp has to drive both speakers, where a mono amp drives only one speaker or better yet, particular individual drivers in a particular speakers, therefore less load on a particular mono amp vs. the stereo amp. The same logic that tells audiophiles to get separates apply with mono amps vs. stereo amps. To get even more crazy, you want each mono amp on a separate power line back to your circuit breaker main panel and on different phases, not the same. That way loading is split on the different phases coming in. Speaker cables have larger current loading and voltages, thereby having larger power loses on the speaker cables. So shorter the cable the better. The mono amps can be placed right next to each speaker and the cables from the amps to the speakers can be really short. This makes a big difference electrically. Longer interconnect cables don't hurt nearly as much, especially balanced. However, if your stereo amp is well designed and stupidly powerful, it really shouldn't matter much. I have found that biamping the speakers (amp for the mid range/highs and another for the bass, for each speaker) make more of a difference than using mono blocks for each speaker vs. stereo amps.
enjoy.
