Hardware selection opinions

[MegaHurtz]

I've been an HTPC hobbyist for long enough now that I think it's time to build a dedicated HTPC and let my poor, tired desktop take a break. I primarily play downloaded TV shows and movies in DivX format, with the occasional 720p or 1080p TV ep or movie. It works fine on regular files, but it sometimes turn into a slideshow when I am trying to watch a 1080p movie. My current setup is:

Opteron 170 @ 2.4ghz
2gb RAM at DDR400 (2-2-2-5 timings I think)
Asus A8N-SLI Premium
eVGA 7900GTX
Soundblaster X-Fi Fatal1ty
Happauge PVR-150 and PVR-500

What I was looking at is:
AMD 2.2 or 2.4ghz quad core (depending on the price at the time I buy)
4gb RAM
Asus M2N-E
Palit 8800GT 1gb
Silverstone Lascala LC17B
OCZ GameXtream 750w PSU

I am going to be swapping the hard drives from my current system to put into the new one. It will be getting a 1tb and 2 750gb drives. I'll be adding another smaller drive as the system drive, and maybe another 1tb as well. The TV cards will also be going into the new system.

Does this sound like a good setup? I need it to have solid playback of 1080p h.264 and x.264 files. I rely heavily on this thing, so it needs to be a workhorse.

Will I be fine with onboard sound? Or should I maybe spend $100 on a decent soundcard... something that can output 5.1 to my receiver.

[rtv]

*sigh* energy costs must be cheap in your country...

This machine would be almost overpowered for non-gaming jobs. The onboard GPU on ATI's 780G or Nvidia's 8200 boards perfectly handles 1080p.
Regarding the onboard sound: if you use a digital connection you just have to make sure it is supporting 44,1 Khz output for music.