I only use my RM1x to sequence my external gear, as i don't use the onboard synth (not even got it plugged in to my desk).
I use the knobs to control parameters on my sampler (For modulating effects, LFO's etc) and the same for my synths.
Just dial in the relevant CC's and away you go.....
Love the RM1x, use it to sequence everything, and then mix the audio down in Logic.