Newbie looking for a little help to get started... Boss Katana and Ardour

Yes, you are absolutely correct. I realized later that the context may not have been clear, for any tracks recorded later the best approach would be to understand the gain architecture of the hardware device and set it appropriately. The comment about the trim control was just about the already recorded tracks and optimizing the levels for plugins and mixing.
I looked at the owner’s manual for that Boss guitar amp and I don’t see any gain settings for just the audio interface section, it seems to rely on the guitar amp controls that set gain through the rest of the amp.