Yes, this is something we've been asked a few times. The Radeon x1300 is a very basic card for such a machine. I'm able to change it to an x1600 Pro at no extra cost. Also, an upgrade to a Core 2 Duo processor is also possible for a fair price.
As for sound, X-Fi cards are the best, but personally, I can get by with on board sound.
The power supplies are great. I wasn't aware of them being looked upon as 'bad" :| I will take a look at that list, but they have actually been the best power supplies we've used. They are quiet, attractive, and the modular connectors are a great feature.
Contact me through Live Help or email if you're interested in getting this system with a better graphics card and processor for a great deal.