Now we are getting a bit closer …
Remembering that you can only control "knobs" (on screen values)..
So, you want to remotely control the "Chorus" setting on this preset. You press and hold the "Chorus" button. Then select <modulate>. Then you select the modulation SOURCE.
You probably selected <ext1> and then on the externals page, set this to your desired MIDI CC. This would be fine, except that … many of the presets have a master SEND control which controls the volume of the effect, and this is usually attached to ext1. This is why your MIDI control set everything to dry (no effects). It's covered in the manual somewhere, but I can't find it at this time.
So, just use a different external – I would suggest ext4 or above.
