Run digital to a stereo receiver, run bookshelf speakers and (after some research) have a plenty powerful headphone output. That'd get you way more power than a sound card...though it'd take up a ton more room. I had the same issue and eventually gave in and paid the money for my kickass Auzen X-Fi Forte, haven't looked back since...best soundcard I've ever owned. And you might try what Athlon X2 says, but expect clipping to happen sooner if you push the level too high....though it would be interesting to see an onboard sound "mod" to increase output power. Good luck!
