Don't forget to put all those parts into Pricegrabber.com to see where you can get the best deal. Pricegrabber looks over a whole lot of sites that many people would overlook and it occasionally comes up with a price for a product that beats the prices of the 'big' stores (Tigerdirect, Newegg, et cetera).
If you're really set on getting an ATI card, I really can't blame you since I personally don't like nVidia much myself. But if you wanted to get an ATI card that might be worth purchasing, then the X600 and x700 line are out of the question entirely. ATI's x800 GT would be the closest comparable product to nVidia's 6600 GT and anything less than that simply isn't worth looking at for any decent performance. Trust me.
I do hate having to say this over and over again, but...really, at this point you're probably better off getting an nVidia card because ATI has really been backed into a corner for the time being. Not permanently, for the time being. If you wanted to delay your upgrade a little bit longer and see what ATI can come up with when they release their new video cards some time in the near future. I don't know exactly when that will be, but I know that I'm looking forward to seeing what they can come up with because I know they're capable of much more than the dismal performance they're putting on now.
I can't confirm this for sure, but as I was browsing around some forums a while back I came across a post where somebody claimed that the Audigy 2 is nothing more than an Audigy 1 with a few fixes. I have an Audigy 1 and the sound quality is nothing short of exceptional. It's been great for listening to music & gaming and I really haven't found any problems with it. If you wanted to save a little money there, I'd recommend looking into the Audigy 1. It's a fine piece of hardware that definitely delivers.
Other than the above, it looks like you're making a lot of smart decisions with your hardware choices. You're getting the CPU that will help you out with video manipulation and mainstream hardware that will perform well for you when you turn to gaming. Hats off to you for a job well done!