Problem running two sets of speakers

Sorry for the non-audiophile level question but I figure someone here knows the answer.

I just moved in to a summer house that has Niles in-wall speakers in the living room and kitchen, each room wired separately. The wiring to the kitchen runs through a Niles volume control unit (to control volume in the kitchen without having to go back into the living room). I hooked up a couple year old Sony receiver (nominally 100 watts per channel) wiring the living room as the A speakers and kitchen as B speakers.

Here is the problem. When I just run the living room (A speakers) alone, I get plenty of volume with the volume knob at about 1/8. When I run the kitchen (B speakers) alone, I need to crank it up to get volume even with the Niles volume control cranked up as well. When I try to run both, the A speakers die off to nothing while the B speakers are only minimally affected.

Questions: is the Niles volume control unit sucking all the power or is there something wrong with the receiver? If the former, is there anything I can do about it short of cutting the volume control out of the circuit (my wife likes the convenience)? Would better equipment help? Or am I doomed to only running them separately?

Thanks for any advice.

Just a guess that the external volume pot is the culprit. I assume you have tried the speakers w/o the pot? Eliminating this should give you your ans. You may be able to get a better quality vol. control to keep the misses happy; a worthy undertaking,indeed!
Bill- I'm with Avguy, the volume control is the likely suspect. However, check the Sony to insure that it doesn't start to run real hot. The Sony receivers really aren't intended for low impedance loads and can quick overheat, particularly if located inside an enclosed rack or shelf.

You may find that for distributed sound, multiple channel amps are preferable. Parasound, Sonance, etc... all offer small, two or multiple channel amps that are designed for this type of application.

Good luck.
Try running the kitchen speakers (alone) and see if you have the same volume problem.
Thanks for your input everyone. I appreciate you taking the time. I'll try bypassing the volume control next time I'm there.