Firstly, if you're not interested in using this computer for gaming, why are you considering getting a top-end video card? You could save a lot of money by stepping down to a less powerful card, say a 7600GS or X1600. Those cards will also be a bit quieter if that's really a main concern of yours.
As to the motherboard, this
ASUS P5L-1394 should do the trick for what you want. It mentions that it has some special fan system that keeps sound at a minimum.
The rest of the components you want to get should do fine. The sound card built into the motherboard I recommended can support a 6.1 sound system, so you won't need to worry about getting a separate card. For speakers proper, I can only suggest Altec since that brand has treated me well.
Jam it back in, in the dark.
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