It's very difficult to recommend a parts list without knowing your exact usage. AFAIK, all the software uses the CPU only. If you have no need of gaming, the best CPU would be one of the new Intel CPU's like the i5-3570.
*Make sure the chosen CPU has an integrated graphics chip and you can avoid buying a graphics card. If you think you might want to game in the future, get an i5-3570K (or non-K, the "K" means overclockable).
Usually an audio workstation has a DEDICATED AUDIO CARD of some kind, though in some cases these are external.
You really need to go to the above link and Google this in forums that talk about this thing.
*It might even be possible to just use a laptop + dedicated USB audio device but again, I really don't know much about the topic.
Here's another link:http://www.m-audio.com/