Screw hooking your HTPC directly up to the TV. When you go that route you have to worry about getting exotic motherboards, good video cards, a super small cases, super quiet fans (or no fans), etc.
I stopped doing that and shoved the HTPC, the NAS, the set top box, and the rest of that mess in the closest. All the TV’s get hooked up via SageTV’s HD200/300 which are purpose built devices for streaming video off the SageTV server in the closet.
Thus I get a far less flakey system, I get the ability to add multiple tuners, I get the ability to add lots of disk (the lady can chew through a terabyte like you would not believe), and I don’t have to have a computer in my living room.
All and all, it just isn’t worth building an HTPC that actually serves the video to the TV. Let the HTPC do the recording. leave the playback to media extenders like the HD300.
My $0.02