Audioplex makes a line level amplifier that is perfect for this application. We use it in every system just for this reason. It is like very inexpensive and gives like +/- 6db @ 1/3 watt. It retails for $75 the Little amp B. This is just a pc board with pods but a good double sided tape (moose dst100) will keep it on the back or the cable box or amplifier or rack or ceiling...... The little amp chasis version cost more then double. If you are not comfortable with just the pcb you can get a project box at radio shack for $5 and pot it in there.