Hey, check out this bass font:
It was also uploaded to sf2midi.com. That guy apparently made a "very basic" soundfont of his '73 Fender Jazz bass. At 30 mb, I think it sounds a bit better than "very basic".
About your other questions:
Maybe your file is clipping too much prior to rendering. The cheap vst exciter you used is suspect. You might have excessive boosting of low frequencies. Use compression and some E.Q. on the essential instruments of Bt's--drums and bass. Use a good limiter when finalizing the loudness of a track. It's not about radically altering the sounds--unless that's what you're aiming for.