Well…
If your video is connected by composite or component, then all the soundbar would need would be an optical or HDMI input (which is pretty much guaranteed).
If your video is connected by HDMI, then the soundbar will either need optical in, or it would need both HDMI input and output, so that it can pass the video on to the TV.
As long as those conditions are met, it should “work”.
But how well it will work would depend on the soundbar… since most of them are only really approximating surround sound, they generally have less than the full 5.1 speaker set… so it depends on how the soundbar decides to emphasize the differernt tracks. I don’t think you can fiddle with it quite like you can with true AVR systems, where you can decide yourself how much goes to each speaker. It could be better than the WDTV’s stock mix, but then again it may not. Without having one to try, I can’t answer.
Your best bet would probably be to get it demo’d in the store, and deal with a store with a decent return policy for if it doesn’t sound as good when you get it home.
Obviously the soundbar would also have to be AC3 5.1 (and DTS 5.1) capable, but they pretty much all are, by definition… the whole point is to approximate a 5.1 system without having a big amp and speakers everywhwere… it’d be kinda silly if it wouldn’t handle surround sound at the inputs and only accepted stereo.
