Are you just going to be using it as a HTPC or are you going to be gaming on it too? Also whats the resolution of the projector? If you arent going to be gaming or doing any heavy tasks you can save a bunch and get an AMD 720 and a 790GX for significantly less and it will perform just as well and produce less heat.
> 1. Do I need a sound card for good quality 7.1, even though I have the motherboard with toslink and the video card? If so, what would you recommend?
An audiophile would probably always say to buy an isolated card for audio... personally I wouldn't notice and wouldn't bother if your toslink will export 7.1 audio that your receiver can properly decode.
> 2. What do I need to add to this machine to be able to control it with my harmony remote?
You'll want an IR receiver. Most of them are tiny rectangle boxes that connect via USB cable to the computer... NewEgg probably has 50 of 'em to choose from. The Harmony remote will let you choose "Windows Media Center" as a device from their setup program.
> 3. Do I need a tv tuner, even though I won't be watching tv on this screen?
You'll only need a tuner if you want to watch TV. For decoding BluRay or other video your GTX260 will be slickity-diptity. You DO have a $120 BluRay drive on this thing and not just a DVD drive, right?
> 4. Will this home theatre setup work?
It's grossly overpowered but it should work just great. That's probably going to be a noisy setup, however. I just went through my system and spent about $100 on ultra-quiet fans and to get rid of the LED blinky-lights that came in some of the components.