I'm assuming by "gain" you mean the channel trim knob? I haven't experienced the problem you describe, so I don't have a definite answer for you. Perhaps Bose will jump in on this discussion.
I noticed that you've had a couple of earlier threads, one about a master volume issue that suddenly appeared, and the other about channel LED's not lighting. In one of those posts, you mentioned your T8s needing service. Did you send it in? While the T8s may be "kind of" working, this might indicate a bigger issue that I would have Bose service look at.
Thanks for the response. here's the update. The lack of sufficient clipping sensitivity and mostly absent red LED when clipping led to a return. The t8s has been sent in for refurbishing after speaking with a Bose service agent. There is a fixed price repair regardless of problem. I'll report on the results in a month (hopefully).
1. The Master volume thread was solved by changing pre/post volume control in preferences
2. The trim knob: there is sound even when the trim is turned all the way down....I thought this was unusual, and then found that my T1 is exactly the same......must be normal.