Although I use the x-fader on occassion (it does free one hand and the curve is pretty well definable on my X1600), my tip would be to make sure that you have the main output level meter up when starting your mix. I am a sound guy too and “0 dB rules!”. So while preparing my mix, I make sure that the signal levels of outgoing and incoming channel are roughly the same (0 dB with max 3-6 dB peaks) on the channel input level meters. Then I check what level my main is outputting at, say -15 dB average. Then when I start the mix and messing with EQ and bringing in the new track, I keep an eye on my master output level to keep it around -15 dB. That way i can correct when necessary (for example lowering the volume of the outgoing track when I bring the bass of the incoming track back up). This way the total level of sound coming out of the main speakers will remain more or less the same.
Obviously there is no substitute for being able to use your ears to do this, but the master output level will give you an immediate heads up when you are not sure and/or need confirmation of what your ears are telling you.
Greetinx,
C.
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