@PurityS.L.G This might sound obvious when you say it out loud, but when you mess with channel one of the UU, being that you’re saying it’s overly bright, don’t be afraid to set the treble and even mids full counter clockwise and see what happens then. Go nuts with it. Maybe that's unnecessary to say but I’ve seen a lot of people say they have “fully experimented” with amps but really have never turned anything beyond 10-2. Twist those knobs, that’s what they’re there for.
One more other thing to note, I’m not completely sure if the new Uberschall works like this, but every other Bogner amp I’ve played behaves in the following way: the treble knob is audio taper and doesn’t really do anything between fully off and like 1:00, and when the treble knob is set lower than around, say, 2:00, the mid knob acts as basically a high shelf that starts in the mids, so it controls the treble just as much as the mids. In other words, when the treble knob is set to “normal“ values, it's not doing a lot and instead the mid knob kind of takes over everything above the bass frequencies and raises / lowers them all fairly equally. So even if you zero the Treble control you might still get some shrill highs if the Mid knob is too high, but you just never think to adjust it because it's labeled "Middle," you know?
Here are two tracks I made with my Helios 100 a few months back. Both setups were identical except in the "darker" track, the Mid knob is turned down several o'clock settings. That's it. Presence, Treble, Bass, Gain, and Volume were untouched.
Helios Mid knob set higher:
Helios Mid knob set lower: