After I saw this post, I thought that I'd add my 2 cents. I, too, recently wanted to share my pc speakers with multiple devices. In my case, I'm trying to share a pc speaker set among 3 computers. So far, I've managed to do so by using the following:
1 audio/video selector switch (4 input /1 output) RCA connections cost: $20
4 3.5mm stereo male to RCA male Y-cable cost: $4/each $16 total
I did this because I didn't want to toss the KVM switch I just bought which si working well. Anyway, I got all of my parts via eBay. My total cost was $36. This configuration works fine but I think a little power is lost when more than 1 computer is running. I just wanted something that'd allow me to share 1 pc speaker set vs. 3 speaker sets on my desk.
Only other inexpensive option I could fathom would be to connect all of your devices to a stereo with multiple inputs (DVD, VCR, tape, phono). I could have done this too but that'd require buying speakers & a subwoofer. I hope this information was somewhat helpful.