For future reference, I found the (now obvious) cause of my quiet and inconsistent voice volume:
I was monitoring the Xpander from _just_ the Right output, but the reset/default Pan settings spread the voices across the outputs. E.g. The quiet voice #1 was actually fully panned to the Left, inaudible from the Right output.
The other voices incremented in volume from 1 to 6. Of course, patching from the Left output reveals the inverse: Voice #6 is quiet and the others increment in volume from 6 to 1. Patching from the Mono output, all voices have same volume.
So, lesson #427: Doing a reset (holing clear at power up) sets the Master->Pan voice settings to the default: LEFT-LF2-LF1-RT1-RT2-RIGHT. If you are monitoring the Left or Right output individually, the voices will sound from progressively quiet to near silent.
Possible solutions include:
-Monitoring via the Mono output.
-Monitoring output from Left and Right simultaneously, i.e. via a mixer.
-Setting the Master->Pan settings to MID-MID-MID-MID-MID-MID. (Of course, these settings will be set to the defaults again if you do another system reset.
Now, back to my tuning problem...