Skittle is right. I'd add one of these cards:http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&DEPA=0&Description=HT+Omega&x=0&y=0
OK, try the onboard first, see how it feels.
I'd change the HDD to WD6400AAKS. You get 640GB instead of 250GB for a few bucks more. The WD is also faster at reading/writing large files, which I guess matters for audio editing. Also, I'd get two disks, because some editing operations work much better if the source and destination are on different disks.
The rest of the build is actually perfect, IMO.