What gear does your signal go through before it enters the soundcard?
A soundcard normally does very little to alter the sound. Of course expensive ones will sound better, but if your signal is decent before it goes into the soundcard, it should not be deteriorated to the extent that you lose all of your tone.
Just find out what exactly ****s up your sound before you go buying new gear. And like I said, it's probably not the soundcard(if you're recording at 16bit/44.1kHz that is).