Recommendation for Computer/Digital

So I've been doing research into various solutions to my issue- most of my music is on my computer. I don't have a pretty low-end CD player right now and instead of spending money on a decent player I have been exploring computer based audio solutions- Squeezebox, Roku, new soundcards (M-Audio etc.). I have a laptop and its internal soundcard is all I have.

I've been getting caught up in the idea of a squeezebox right now, and with the cost of mods it's getting out of my range. I'm looking to spend up to $500 max. An M-Audio transport, which is the basis of the Red Wine Audio USB Select solution (a $500 solution) costs $99. I'm having a huge problem in figuring out how the variety of solutions compare and where the most bang for the buck lies. I've even been using my XBOX as my digital music player for awhile now.

My request- your views on the best way to get great sound in my price range from a computer with a crummy soundcard. Personal experiences are greatly appreciated. Is a stock Squeezebox a good thing? It seems that all the raving is from the modified end.

My system so far: I have a McIntosh MA500 Amp and B&W Nautilus 803D speakers (I think that's the right Nautilus model- I'm away from home for several months for work). Any suggestions to improve that would also be appreciated. I'll admit I bought without knowing too much- my wife's ears were the main reason we ended up with what we did, even though I'm more of the music lover.

Thanks for any responses.

Nick