Looking for better sound from my Dell XPS

If your budget it's tight (or not), I strongly suggest you to get an EMU 0404 USB 2.0 interface. It has a good internal clock (that reduces jitter) a great DAC, and it's 24/96 capable via USB. I had one and I loved it. For about $200, you won't have many better choices.
http://www.emu.com/products/product.asp?product=15185
Cheers

Lucho

I forgot to mention that the EMU works with ASIO plugins, which allow you to by-pass the K-mixer and get bit-perfect digital audio out of your computer. I suggest you to use Foobar or Media Monkey as media players.
Luciano

Thanks Lucho.