ooops... this is MHO so no flames please..

I wouldn't use the gains at all... use the gains while u cue / pfl a track 'till u get ruffly the same vol in each channel .. then use the fader or even the x-fader... the gain can b very fast and very intense... sure u can get used 2 this method and get as smooth as u want but u get another mixer in front of ya nad its certain disaster...

A gain pot can generate a very big change in volume, U'll notice this with a brutal fact if u r playing on a big system!! (not so much at home !!)

Again this is my experience and personal opinion, so follow the method u feel workz better 4 ya!!

Z