USB Speakers Cutting Out Sound Card

I have a Line X FM transmitter that plugs into a USB port
and allows the PC sound to picked up on any nearby FM
receiver. It works OK. Problem is the system sees the
transmitter as a pair of USB speakers and cuts sound to
the sound card.

I can see this is the "normal" set up you would want for
USB speakers but I'd like to listen on my PC in one room
and have the sound on elsewhere too.

I running XP, ant work arounds you coan suggest I'd be
grateful.

Thanks,

Peter