All look like good choices to me... I'm running MCE 2005 on a 6600GT and a HT P4 @ 3Ghz and its great. The Abit mobo I use has SPDIF ins and outs right on the board and I think the sound from movies (DVDs) and music sounds supurb.
Now if they wouldn't have moved Vista back till 2007 grrrrr...
FYI to my knowledge the only passively cooled 6600's are the PCIe version because they use an extra chip on the AGP ones and it generates extra heat and requires a fan... that said the one shown above really looks like a great passvie cooling solution.
