Need advice on whether to upgrade my HTPC's nVidia 7600GT card

The basic specs for my HTPC:

HP m7790y media PC
Vista Home Premium SP1 (32 bit)
Intel Dual Core 6600 @ 2.40 GHz
2 GB RAM
nVidia GeForce 7600GT (PCIx) -- connecting to a 67" Samsung DLP via DVI -> HDMI cable
SPDIF out to AVR (coaxial)
TheaterTek (player of choice)

My system is very stable, and I really don't have any complaints. But I was wondering if I could improve things by upgrading my video card. I am not a gamer; I use my HTPC exclusively for music and video, watching avi, dvr-ms, and mkv files (mainly mkv's). I also have an HD-DVD internal drive (basiclly the same drive that's in the xBox), which I don't use too often because of the crappy proprietary software that came pre-loaded (major overscan); I'd rather use my standalone player.

I had some stuttering issues with some 720p and 1080p mkv files, which were pretty much eliminated by changing from Cyberlink's decoder to CoreAVC. Some vids still show a minor hiccup right after a scene change or with horizontal movement. I'm seeing the following CPU usage:

avi (Xvid decoder - EVR) - 15-20%
mkv (CoreAVC decoder - VMR9) - 25-30%
dvr-ms (nVidia decoder - EVR) - 35-40%

I can't find anything definitive on the web whether the nVidia 7600GT is HDCP compliant or not. I assume it must be, if I can watch HD-DVD material. Also I'm not sure if the card is DXVA capable or not (I've read conflicting reports). I've read so many posts comparing video cards, ATI vs. nVidia, and also different models within one brand, that my head hurts.

So my basic question is: for those who use their HTPCs for viewing video, what would your suggestions be? Would a card upgrade -- for instance to an nVidia 8600GTS, or maybe 9500GT (overkill?) -- make my system more efficient and produce a better quality image? Or should I just leave well enough alone?

Thanks.

The audio over HDMI would be great and I wouldn't think twice about it, except my AVR can't pass 1080p to my display, only 1080i. Some say that's not a big deal; I honestly don't know how much of a sacrifice that would be. I like the idea of sending 1080p directly to the TV; my audio setup is 5.1 (not enough space for 7.1), and I've always felt SPDIF was more than adequate since all of the video I watch is no more than 5.1. But it wouldn't hurt, I suppose, to get the ATI and have the HDMI option there in case I have a change of heart.

EDIT: Also, my power supply maxes out at 350W. Is this adequate for the 4670 or the 9500GT?

One more question: Sapphire vs. Gigabyte 4450? Any major differences between the two?

Yeah, typo. Meant 4550.

Comparing the specs on Newegg, it seems the cards are pretty much identical, but with the Sapphire being low profile. I read other threads as well and caught that comment about cooling. My case is ventilated well and I don't need a low profile card so I went ahead and ordered the Gigabyte from Newegg. The Gigabyte also has better manufacturer's warranty, which hopefully will be a non-issue.



Thanks for the input. I think if I were more into gaming I would have considered the 9600gt more, but it appears the 4550 will be perfect for my needs and, at half the price, hard to pass up.