For what it’s worth.
In Song Mode, set up 16 different instruments. On 1 and 9 the same basic instrument.
In your Daw (I use mainstage for this) make tracks using all midi channels except 1 and 9.
Motif: local control has to be on otherwise faders don’t do their job.
Put your motif in mix mode
Now, you can play and switch, up to 15 sounds on 15 different midi channels, with independent volume control with the motif faders and possibility to mute tracks/midichannels
If you need the faders for midi channels 9-16, you have to push track button 9. That’s why it has to be the same instrument as 1 unless you want an other sound.
A simple laptop will do, because it’s only midi you use, no soft synths.