I would invert that. buy an expensive GPU now and wait for an expensive CPU later. As of right now most graphics cards are cpu limited.
The other consideration is that because the r580's and g70's cores are I believe will be shipping in a few months I think. It is a bit of a conundrum as to which way you should swing.
Do you really want both speakers and a headset? I would imagine headset is for gaming and speakers for movie watching, but you might be able to consolidate both those and use either a headset or speakers alone. If you do want both, I would recommend the HD497's from Sennheiser, I think you can get them for less than $50 bucks at newegg. I have them and they are exceptional, very comfortable and they sound great, I am not an audiophile but they seem to like em as well. Also consider checking out this thread
http://www.ocforums.com/showthread.php?t=383298 for some options. I can't however, make any recommendations on speakers.
For the processor, I would recommend either an opteron 148 or an a64 3700+ as they are nearly the same price ($220) and both have 2.2ghz clock and 1mb l2 cache.
Since you don't want a DFI board, I would recommend Asus, Abit or Epox, but I have no idea what the best boards are from those companies.
With video and music edititing I would imagine you would get lots of benifit from 2gb of memory. I would suggest looking for 2x1gb sticks of good memory. Mushkin, Corsair, or OCZ have good offerings.
For storage I would recommend picking up any 200gb Sata drive. I would get one that supports SataII (as well as a mobo). And then once you get your extra $1000, probably pick up another one, if you are doing any editing. Some people might recommend getting a Western Digital Raptor for doing any editing and such, but I personally think they are overratted for the price and storage space. Some people swear by them however, so take that with a grain of salt.
If you get any case, I would make sure that you do not get one with a psu, as all the ones that come with them are crap. So save yourself some money and pick one without it. There is a deal now on newegg for a Coolermaster Centurion for $45 I think, and that is a pretty slick case.
For the power requirements of your system I would get either a decent 450ish watt psu or go straight for 500+ watts o' power. I would imagine that most people will recommend anything from Fortron or OCZ if you want to spend a bit. the forton AX500 I think it is, is a 500w? psu that is pretty good, I didnt get it because It has dual +12v rails and I didnt want that. I got a Sparkle 550W Psu for $103.50 from newegg that is a very good psu. Also make sure that your psu has the right connector for your mobo, Some have 20pin+4pin or 24pin atx connections. I didnt want to get an adaptor so I made sure they matched up.
Monitor I would look around the Display section for. most 19" LCD's that are decent go for between $250-300 some. So I would budget for that. If you want a CRT they are cheaper but I don't know of any prices.
Good luck with your build!