In simple terms, modulation of power supplies refers to the effect different channels drawing from a shared power supply has. This may not be as big an issue with stereo amps that are "dual mono", or even to a stereo amp that has a very robust power supply. Proximity usually refers to the potential for channel cross-talk amongst other things, such as power draw, heat dissipation, placement ease, etc.. The ultimate sound is the most important factor involving amplification's sound. Seperating the channels is only one aspect of designing an amplifier, and certainly not the most important one, as Atmasphere and Czbbcl have wisely pointed out. As I said, if all else is equal there can be advantages to mono amps, but, in and of itself there are many other important considerations, especially when there are budget considerations. That is why I use a stereo amp, even though, I appreciate the advantages of mono amps. As to the relative lengths of interconnect vis a vis speaker cables, there are differences of opinoion here as well. Decisions as to relative length may be best determined, specificaly to each system (including the specific cables). Personally, I usually prefer to use shorter interconnects and longer speaker cable. There are some other advantages to mono amps as well,that again, in themselves don't necessarily make them superior. I humbly suggest you review the archives. You will find a quite a bit of discussion on mono vs. stereo amps and short/long interconnects vs. short/long speaker cables.
