A few solutions, although I'm not sure what your receiver alows you to do as for as pre-outs and ins. My first suggestion would be to spend about $35 at Rat Shack and get a SPL meter. You should be able to calibrate your channel outputs to make everything "even". Second, if your center channel speaker is bi-ampable - use the two freed-up channels on your receiver to bi-amp the center channel (I'm doing that with a 2-channel amp with great results). If you want to go through a speaker selector switching box, Niles Audio makes several versions. Though not "true" audiophile grade, they are pretty darn good! Good luck!
Switching device for speaker source
I have a A/V 5-channel 75W receiver. Now I'm auditioning a 2-channel 185W amp. I noticed the volume from the amp is way higher than from the receiver. This may cause imbalance between the central-channel and LR front speakers when playing DVD movies. Is there a device I can connect speaker wires from both receiver and aml to it and select the source depending on whether I listen to music or play HT stuff? What's its cost? Does it have any side-effect when doing so? Thanks. Mike C