Thanks again. Yes, VU meters seem to be the one type of output-only mapping that is available. And from Jay Neural’s work (see above), I discovered that we can map mixer.masterLeftMeter and mixer.masterRightMeter as well as the turntable monometers.
However, it’s still a little limited. This maps well onto a dedicated hardware VU meter, by less well onto an arbitrary series of LEDs. Again, Traktor’s Controller Range is useful here - allowing, say, high values to be mapped to a red LED, low values to a green LED, and middling values to a yellow LED.
Will definitely check out your site though, to see if there’s anything else I can use…