Das Problem der geringeren Lautstärke nach Updates ist wohl bekannt.
Schau mal hier:
Fix low volume after updating Roland TD17KV(X) to version 2 – Purple Serendipity
Lösungsansatz ist aber auch hier einfach die KIT Lautstärken zu erhöhen.
Hier gibt es zumindest einen spekulativen Erklärungsansatz:
https://www.vdrums.com/forum/general/products/1284220-td-17-2-0-headphone-sound
"I read a while back that someone emailed Roland about this after it happened on an earlier update (possibly 1.02). According to their response, there was apparently a bug before that update where the last 1/3 or so of the volume dial didn't actually do anything - the full volume of the module would be hit at around the 2/3 mark. They fixed this bug and redistributed the volume across the entire dial. So apparently the maximum volume is supposed to be the same but if you previously set your volume to 2/3 of the dial, now you will need to max out the dial to get the same output volume. Some people didn't update to 1.02 so will probably be experiencing it for the first time on 2.00/2.01."
Vielleicht hilft das, nochmal genauer nach Lösungen zu suchen.