Tough audio wiring problem, need expert adv.

I have a Archos AV500 with a copy of my entire collection of music. I often like to listen to music in my dorm room while I fall asleep (without using my PC).

I want to connect the AV500 to the 5.1 setup (which is also conencted to the PC.) The 5.1 setup only has 1 input. Additionally, I would need to clone the stereo out from the AV500 to the rear speakers of the 5.1.

I have Y-splitters but those would also feed the AV500 signal into the sound card (possibly bad?) and also, that wouldn't allow me to clone the front to rear and maintain proper operation in normal 5.1 mode (becasue the seperate channels would be physically connected always in such an arrangement).

What is the best way to do this?

I was thinking diodes but I have no idea what that would do to the audio signal.

One input means one input. It will always be a mess unless you install a switch somewhere.

By one input do you mean one plug / socket (with multiple channels - if so how many?) or just one channel?

Diodes will fuck with your signal, cutting half the waveform so it sounds clipped.

What sort of input is it?  Optical, or RCA/Coax?  The latter can be served by a cheap switchbox.  Check your loca Ratshack.