One thing you can use when going troubleshooting is those level meters you have at various positions in Live. In that example shot, you have:
a) the meter next to the "All Channels" text on your "keys" track - this is what comes into the input interface for that track.
b) a meter on the left side of your piano synth - this is the MIDI data that goes into the plugin (not necessarily processed by it, though)
c) a meter on the right side of the synth - that's the audio going out
Actually lookng at these was quite useful, I managed to figure out that there WAS midi getting all the way thru all plugins...
Then I remembered...
you said...
Then you need to check that the track the synth is on is selected for
recording or for monitoring - I guess you already know that, just to be
sure...
and i said...
Actually not
really... no checking if I see what you mean here... I dont RECORD at
all yet in Abelton, so I have no understanding of it in that mode.
So I investigated THAT.. and sure enough, it works AS EXPECTED, IF I use the tiny ARM SESSION buttons to select the channel.
What I dont undrstand, is that previously I did have it working where I dont HAVE to select that tiny button, but could just move focus (using crsow keys if I wanted) onto the next channel...
The reason I remember this was the case, is that I once had fun, soloing woth the right hand on my keyboard while using the left to swich back and forth between sounds, and getting quite a cool patch changing effect...
So... Im still a bit in the dark... but... at least its working..