Request For Assistance II: Wireless Speaker Retrofit

Thanks to those of you who responded to my last request for assistance. Here's another one for you. I'm setting up a 5.1 surround speaker system, driven by a small form factor PC running either Windows XP Media Center Edition or Vista Home Premium/Ultimate (I haven't decided yet….and a Mac mini is also a distant possibility). I'm unable to run speaker wire to the rear-channel surround speakers, due to some ideosyncracies of the room where I'm installing the gear. Instead, I'd like to broadcast the rear channels' line-level audio content to the corresponding speakers either wirelessly or via a powerline connection (there are AC power plugs handy at both source and destination).

Ideally, I'd like whatever widget is at the receiving end of the audio transmission chain to also contain a two-channel power amp, so that I can go with conventional passive speakers. And of course, I'd like whatever setup I end up with to be high quality and low cost. No powerline-induced hum or interference with my 802.11g network, thankyouverymuch, or perceptible resultant delay between front and rear speakers either, and wide frequency range is also desireable as I'll be using the rear speakers not only for movie effects but also surround music auditioning.

Aside from some proprietary stuff made by companies like Panasonic and Sony, which (surprise!) works only with the same company's A/V receivers, all I've uncovered so far is a wireless speaker kit branded by Rocketfish and sold by Best Buy. Unfortunately, my past audio-over-CAT5 research isn't terribly helpful in this situation, because I can't run CAT5 cable, either. Suggestions, folks? Thanks in advance!