I think a large part of the problem is the C90 speaker. I have a good tone now using the Mark I mode. It’s very similar to the Mark IIC+ mode, more gain, slightly darker. This is how I have channel two set
Mark I
EQ off
90 watt
Thick On
G 12:15
M 11:30
P 2:00
T 2:00
M Off
B 9:30
Effects loop...