Sound issues with my mini

I got a mini when they first came out.. upgraded the RAM and HDD to 512mb's and 100gigs. It's still running 10.3.9. I use an m-audio sonica theater USB sound card too.

Yesterday my roommate and I were listening to music, and he said that it sounds washed out. I compared his music to mine (same song) and lo and behold, he was right. Mine's washed out. Now I use an external sound card.. so I plugged the speakers into my mini's audio-out port. still washed out. I tried the speakers plugged into my iPod, and they were fine. I tried my sound card on my PC and it was fine. It's only from my mac... I tried deleting all the com.xxxx.plist files I could find that had to do with sound and audio, and nothing helped. it's still all washed out. It does this when I play music through iTunes and RealPlayer.

anyone know why? I'll try to check as often as possible, but internet's down in my dorm for the week and I can only get it while I'm in class....