Try this if you're using Realtek HD (may work with other sound devices too, unable to confirm).
Set your speaker config to 5.1 even if you use stereo speakers or headphones (don't worry you don't miss out on any sounds, you get the "front" as well as "rear" channel sounds) and you actually get a bit enhanced surround sound like this compared to using stereo speaker setting (try hitting the test on that page and it sounds like the sound from rear speakers as it would come further back). If I had been using Realtek HD onboard as my main sound device I would always use 5.1 speakers even for headphones/stereo speaker setups as it simply sounds best like this in pretty much any cases anyway.
Picture: [img]http://img825.imageshack.us/img825/6879/realtekskyrim.jpg[/img]
EDIT: I also want to add that I get the best volume if set the output device to 44100 sample bitrate / 24bit playback (but the difference is small).
I would still like to use my other soundcard though but this will have to do for now, with the headphones I tested even 35~40% which is about normal volume when listening to music sounded sufficient ingame now! You get very good / normal volume level like this. Looks like Bethesda really has optimized this game for 5.1 use eh?