I've run into the same problem, except my two channel amp is of the tube variety. There is a definite difference in sound (at least to my ear), hence the need for switching. I took the cheap way out and just plug and unplug when switching between HT and stereo listening. Not very convenient, but at least my speakers are easy to get to (their on stands). I haven't looked very hard for switch boxes because from the little research I did, I couldn't justify spending the money on a good one. Right now, I'm the switch box. And relevantly inexpensive, at that.
Having said all that, if I come across a good quality switcher for cheap, I'll be all over it. Or I'll just buy another pair of speakers
. Not the logical choice, but one can't have too many speakers, right?
