Well, let me just say that a few months ago I splurged and bought a $200 Asus Xonar Sound card for my computer. Previously I was using the small PCI 1x 7.1 sound card that came with my Crosshair Mobo.
I have never, EVER been happier with a single upgrade in my life. I was skeptical that I would hear a difference, but the sound difference was absolutely incredible. I really can't even begin to describe it. Maybe I noticed it more with my z5300e setup, but it was absolutely amazing. I had just watched Transformers (we use this computer as a media center) and I watched the battle scenes again and it was completely different. Even regular music sounds much better. What this card did was help me discover the new higher-frequency sounds in movies and music. But everything else ALSO sounds a lot... crisper? I absolutely recommend a good sound card to anyone who wants good sound. These speakers are "THX certified..." and I was never that impressed (I've had them for two years.) I finally understand what this sound system is capable of with this card now.
Also, I used to not be able to go above 75% on the speaker controls without hissing (as with any computer speakers usually.) I assumed that was just normal. Not anymore! 100% and absolutely no hissing or background noise at all.
All in all, I have to say, I would never have expected it, but these things make a phenomenal difference.