Why not go with one of the older video cards, which have fanless coolers on them, like
this . It can play HD content at 1080p, has passive cooling so will not make any noise, and has a UDV for blu-ray and HD DVD.
If you got this this(or something like it) then your mobo would no longer be limeted, but out of the two mobo's you chose I would have the XFX.
For playing media, is the Q6600 not a bit of an overkill, and would it not be better to go for a cheeper dual core CPU, such as one of the 45nm wolfdale CPU's which use less energy, and make less heat, so less fan noise = better Media centre PC. You could get this
E8200 for about the same ammount as the quad.
4gigs is the sweet spot at the moment, but if its only for media playback, two should suffice, i think