I am no technical expert, but seems that one possible answer is obvious. Have you ever experienced "bleed-through" of one source to another? IOW, you play a CD while the preamp is set to "Phono" instead of "CD" or "Aux" and you can hear the CD player's output faintly. Now, a really good design should keep that from happening, but the point is that there is probably the possibility of similar effects occuring in situations where two channels (stereo power amp) share a chassis and at least some of the componentry thus reducing the total separation of the channels that one gets with mono blocks.
We need Al for a better explanation of might be happening.
Al, you out there?
We need Al for a better explanation of might be happening.
Al, you out there?