HP Desktop 500-281 - Sound Quality Setup help

64 Bit operating sysrem
Windows 7 - Home Premium
RAM - 12 GB ( I had my homie RAM my work workhorse up to 12. I use almost exclusively Excel, Word, Adobe and having many different internet windows open - I do legal research all my memory is basically free)
Sound quality that comes standard is actually really solid but I’m looking to turn this computer into a semi-professional, really basic cut/copy DJ setup and professional quality listening while working.
I have a great set of headphones - Brainwavz HM5 Studio Monitor Headphones - $130 bucks. Brainwavz is an incredible company, professional quality headphones, at a realistic price. I have two in ear headphones from them as well for travel and they are immense. In 10 years of really jammin tunes, these are the best cans I ever used, for the price and we all know headphones double and triple in price to these can sometimes be absolute trash. If anyone has any other similar in price to these specs, please post. I like the Hm5 because they are so frickin neutral in the sense, they let the music do the talking and just produce a clear and sharp sound, regardless of genre. I listen to mostly Progressive Trance and Reggae and both sounds work great with these.

I got $500 or so to spend. I just really want to be able to listen to CD’s and digital downloaded, professional quality trance music on my desktop and eventually, use audacity to cut copy my own mixes for fun. I know a need a couple pieces of external hardware at least but rather clueless and tech wise, borderline retarded. The simpler, the better in my case.
Thanks so much for any help. This site is the truth. One

-RS

Do you want to scratch and do you need it portable? If neither, I wonder if you don’t need any other hardware. You can produce multi-track just in Audacity. Koz