i had the same problem once, and i was going crazy thinking that the problem was a software problem. i used a motu midi express xt for a long time and i felt that my midi was in time but it was just a little bit sloppy even using quantize. i even thoutht that my emu modules were acting like that and it started getting worse when i started using newer versions. i had distortion in my audio tracks, i had clicks and pops, my midi tracks would go out of sync. then i discovered that the audio would play right when i turned off my midi tracks and viceversa. so i changed my midi express for an edirol m-800. and all my problems disappeared.