HTPC and video card for encoding

I'm looking for information regarding using a video card for a HTPC and/or encoding video.

I understand the best choices or two very good choices include ATI's HD 2600 and Nvidia 8600 GTS. Those are the high end cards for that kind of video work.

My main questions:
Is it possible to get HDMI audio/video from a Nvidia 8600 GTS? If you buy a DVI to HDMI adapter, can you get the audio from HDMI?

I know you get it with the ATI board as they include the hardware but if you had the adapter separately, could you use it on an Nvidia 8600 GTS board?

I also wondered if the ATI 2600 board can be used in Linux. I went to the ATI website and there doesn't appear to be any drivers.

I am leaning towards the Nvidia board just for having more options.

Either will be fine for playback. And like Rodney said, get passive, great idea for both sound and reliability (no fan to break built with big heatsink).

As for encoding it will depend on the app you se and what kind of encoding you want to do. Generally it's more about the software and it's interaction with the CPU and RAM and HD speed more than the graphics card. some have VPU assisted encoding, but it's a minor part, and often the video card is actually just a pass key that allows the software to work on you system, doesn't actually assist. But other do a bit (still small bit) to help. Most importantly the graphics card will help previews, not final renders.

For Linux yeah go with the GF8600 ATi Linux support lags a bit.