Sound Quality with External USB Soundcard

I have a Sound Blasters MP3 external USB card and when I first installed it, the sound was very nice - tight bass, good sound quality - great volume! However, recently I noticed that my HU which is wired to the same amps has a much better sound. Cleaner bass, louder volume, etc. The sound card seems like it is worn out. Is this possible? I only bought the $40 one, so that could be my fault. Any ideas? I have the PC volume set to 100% and I have heard that can cause problems - but the sound quality has just gone down. Any help is greatly appreciated!

P.S. Anyone in the San Diego Area?

Did you try using line drivers?

excuse my ignorance... what are line drivers?

it basically drives the line, the output voltage on your card is probably below 1volt, a line driver would make it a higher output voltage, which would give you a cleaner signal without turning up the gain to adjust for it, which causes distortion, most HU's nowadays already have a nice output voltage...3-6 volts usually, so headunits dont require external line drivers because they have them built in!