Hard to tell what the problem is without actually hearing a track, but sometimes a tad of short reverb at moderate mix levels can help give a little more "naturalness" to an overly crisp vocal track.

If the volume is jumping all over the place, it's hard to get it to sit in the mix because loud passages leap out and grab you in the nuts, while soft passages get lost in the mix. Experiment with a couple of compressors with different settings - start with moderate attack and release times, 3:1 ratio with the threshold set to affect everything but the quietest syllables.

If there's a ssssssibilant problem, try using a multiband (I believe the Sonitus FX suite has one... never really used it much though) to rein in the ss and tt sounds.

You could also try this trick - send the track to an aux, band-pass (again, experimenting works wonders here, but generally choose a frequency range that isn't already being saturated in the mix) and compress the heck out of it, then ease up the aux behind the main vocal track. This is so that the track maintains it's dynamics, but still "sits above" the music when the volume dips.

These are a few tricks that have worked for me at various times. Sorry if I'm repeating basic stuff you already know. ;)

All very good tips. You might also try running an aux to an amp sim and feed it everything but the low freq sounds (bass, kick, etc), and giving it just a slight PA sound, nothing radical. David

Also try this:

Run your entire beat through a bus. Place a parametric eq on that bus and scoop out the midrange slightly. I normally try a 1-1.5dB reduction centered around 1 or 2kHz with a wide Q range (lower Q = wider band). This allows the vocals a space to breathe (no pun intended)

Also falkon2's sideband compression trick is a favorite of mine. falkon, did you know this technique was supposedly developed by Motown?

mitz