Wireless Speakers/Home Theatre Doesn't Work on AUX

I have a home theatre unit that I'm using as a stero system for an AudioTron (plays MP3 from a computer). The AudioTron is hooked to the home theatre unit through the audio in and is played using the AUX selection. I hooked up the RCA 900MHz wireless speakers to the home theatre unit through the audio out. The wireless speakers work fine if I'm playing a CD or the radio; but they don't work if I play the AUX. Is there something about the AUX not operating the same as the CD or radio because it isn't part of the home theatre unit?