There are many ways to get to Rome and i think, you will get some other solutions here.
But perhaps as an alternative to MIDI and perhaps much simpler, using a (double) footswitch would be interesting for you.
For example, you could save your volumes in 2 different scenes and select them with the 2 foot keys.
(However, CQ does not yet have the option of just changing the fader positions using a filter; you would actually have to switch between 2 complete scenes.)
Or, if you don’t use a compressor yourself, you could switch a 1:1 compressor on and off in this channel, with which you can achieve a level difference of up to 18dB.
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