I'm getting ready to build my HTPC and if my Radeon 5830 fits I'd like to use that card as it has a dedicated HDMI port (this build will be hooked up to a 55" 1080p TV with BD-R online content and web site video streaming in mind). If not I've got a GTX 550TI that I know works with that power supply but it doesn't have a full HDMI port - only a mini HDMI port.
If it helps this is the motherboard, case, and PSU I'll be using in the build:
Guru3d review suggests that you need 35-40A on 12V rail and xbitlabs measured 467W of power draw (linpack + furmark), but both reviews use heavily overclocked lga1366 i7s.
All in all, I think it all depends on a cpu you are going to use and its OC level.
I guess you don't plan > 4GHz overclock, and those 170W is a extreme situation (furmark etc), so for normal usage even with some gaming I think this PSU is enough.
I was just thinking of something heavily taxing for the card, and Crysis came to mind.
But the same principle applies. Try playing a few HD movies and see how it goes.
Aside from the power though I'm also wondering how that's all going to fit into the case. The Radeon 5830 is a 10.5" card and Silverstone says the case is rated for cards up to 12". I'm wondering how tight of a fit it's going to be.