I would drop the sound card, unless you have a good set of cans to back it up. Extreme4 is a solid board, I would keep it A quality 500W is plenty for your setup
Here is a link to a high quality modular psu
With the savings you can probably up the GPU to a GTX 670 or pocket the difference
I will be upgrading my headphones to Audio Technica ATH-AD700s later this year. The sound card stays.
How different is the Pro3 from the Extreme4?
I will consider the PSU.
I'm not changing the key parts like the GPU or CPU. I need to tone down the price.