My mistake, you are right, I just checked the sound settings and the balance is not available with bass/treble, I was pretty sure to have seen it somewhere in the app.
Thanks for the info regarding the black lamellas, I will check with my dealer, but as the frets are coming separately it should be possible to order them or find a way to get them, if ever one of them is breaking during the warranty period, they might have some stock available.