You can either find a receiver/amplifier with a mono switch or you can buy a stereo-to-mono transformer. You'll have to decide which is more appropriate to your situation. After that you'll need a switch box with volume controls. If you wish to have all the controls in one location, you need only a box which contains both switch and vc. Niles and Russound plus various other companies make such products. Check with any audio shop that does home automation installations which would normally include most home theater oriented shops.