Hiya Zilch99
I’ll try to help a bit.
Firstly CC11 is expression as you say, but CC7 is volume. some synths and some patches will vary with CC11. It may not change the volume, but it may change the timbre or “mood” of the sound.
Next, are you taking about the midi faders on the mixer, because they are displaying velocity by default.
Not sure how you would do the task you’ve set out to do, but this link may be of help.
Have a wade through it and the tips I’m thinking of are start at the top of page 2.
Hope it helps
Neil