I have no experience with Avcast, but I did think it was very intriguing when I first saw it a year ago. I did talk to my local HT retailer, who's opinion I respect, and they said it was of generally poor quality.
What you're really looking for is channel modulation plus IR distribution. There's no doubt that Avcast does it simply and cheaply, but I'm not sure how good the results would be. I use a Channel Plus (model 5435) modulator and Xantech IR distribution products to distribute three sources to 4 TV's and it works very well.
Remember, most of the modulators including Avcast only distribute a mono signal, so if stereo is important to you, you'd have to go with stereo modulators, which are more expensive.
Hope this helps.
Trying to figure it ALL out (and hope I never do!!)
See my HT at www.citycinema.s5.com
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