It's one example of a drawback when you...

...go with Vizio instead of a better supported brand. That would be your next test- bring in an alternative HDTV brand, and test it out with your 2 HTPCs. I know it's a pain, and will cost you some $$, but that's about all that's left since Vizio clearly doesn't provide support as such.

FWIW, it's not the first time I have heard of a Vizio puke on PC content from a supported graphics card output. <shrug>.

Did you also post @ avsforum.com?