Hi WYMAN:
There maybe two options, checkout the SSVC1 Speaker selector with built in Volume Control. It has dual source A or B input. And an on /off switch and Source A or B switch as well. Plus a volume knob to attenuate the volume level. basically you are turning the sound down, there is no gain. The other option is using our SVC-405 Volume Control that has two stereo inputs and a single stereo output. Both options will switch between your two receivers.
TL/4273