Pleased that we've been of assistance, John.

(I think) I can use conventional stereo audio output (panned to 0 and 127) PLUS I can send at least one channel to my puny MIDI keyboard - maybe two 'cos it's stereo.

Absolutely. There's no reason why you shouldn't get two discrete channels from your external keyboard using midi panning. As it's 'puny' it's probably only got a single stereo output, but splitter cables that will allow you to send each signal to a separate speaker are easily and cheaply available.

Let us know how you get on!

Ed