Surround sound problems.

I've been having some problems with my surround sound on the GTD-120 using external audio inputs (aux1) from my Xbox 360 (and other game consoles).

Basically, when I power up the GTD and go into the DVD playback mode, everything works great. However, the second I switch to aux1 (or aux2), I lose everything except the front left and right speakers and the sub.

Now, after switching to aux1, upon switching back to DVD, the back and center speakers still are greyed out, and produce little or no sound. I've checked all the connections, and everything is fine (hell, everything works great UNTIL I switch the GTD over to aux).

What I'd really like to know is if the GTD 120 even supports dolby 5.1 from the aux ports, and if so, what is my problem and how can I go about fixing it. If it doesn't support 5.1 from the aux ports, then if anyone can suggest another reciever that DOES support 5.1 from the aux ports, for LESS than $150, and is NOT made by GE, that would be great.

Thanks