|Pop in a DVD or Blu-ray and you'll get surround sound.|
Most music isn't encoded in surround, so you'll have to upmix to 5.1 using Dolby Pro-Logic (or a similar algorithm). I haven't used the analog audio outputs on my PC for a couple years now, but iirc, the audio driver did feature Dolby PLII upmixing.
If your audio driver doesn't allow you to upmix, download AC3Filter and have it upmix the output of a DirectShow player (for example, MPC-HC). You'll have to ditch iTunes, which is a plus--that bloatware makes Windows Media Player seem wonderfully efficient.
As for the lack of bass--I'm blaming the set's small subwoofer. You could try boosting the low-end with your audio driver's EQ, but that'll probably lower the sound quality.
Socket 939 | Dual-core Opteron 185 @ 3.2GHz | 4GB | 1.0TB | Win7 x64
GeForce GTX 460 1GB | X-Fi Ti Pro | A8N32-SLI Deluxe | Antec P182