Can you not spare 16 notes, to trigger the VST Expression map directly?
If you absolutely must do this via a MIDi fader, this can be done, but it’s a bit cumbersome…
The idea is to send your MIDI controller (let’s say CC#6) into a track in Cubase, and let the track’s Input Transformer convert that into MIDI notes 24 thru 39, which will then trigger the VST Expression Map.
Unfortunately though, the VST Expression map doesn’t recognize the Input Transformer directly, so you have to send that MIDI track (having passed through the Input Transformer, but without any VST Expression map) out to some external MIDI Loopback (e.g. MIDI Yoke, LoopBe or similar… or, if on Mac, the IAC Bus), then use a 2nd MIDI track (output to the instrument of your choice), whose input is the return from the MIDI Loopback, and place the VST Expression map on that track. (you’ll need to record-enable, or at least monitor-enable both tracks)
Here is the setting you’ll need for the Input Transformer…
(Select and activate its 1st module)
Value 1 (MIDI Controller Number)Equal (controller number of your choice, I used CC#6 here)
Value 1___Round by___8 (gives 0,8,16,24,32 etc.)
Value 1___Divide by___8 (gives 0,1,2,3,4 etc.)
Type___Set to fixed value___Note (so, what was CC#6=0 becomes note-on C0/24)
Function = “Transform”
One disadvantage, however, is that, even though there are indeed now only 16 discreet values, there will still be 128 events transmitted by your incoming fader (so, for example, the destination track will receive 8 consecutive notes with the same value).
If your MIDI keyboard can’t spare, say, the bottom 16 notes to use as remote triggers, I’d rather recommend you invested in something cheap ‘n’ cheerful like a Korg Nano Keys, and trigger the VST Expression map from there . (I’m pretty sure that, using the above-mentioned MIDI fader method, you won’t be able to trigger the desired articulation quickly enough )