If you want to reduce the mud, that usually involves cutting the bass going into the distortion stage.
If you want to cut the bass in the BIG channel, reduce C7 or C8. Try a 10x reduction and try them one at a time.
If you want to cut the bass in the TIGHT channel, reduce C1 to 10nF. If that's too much cut, then try 22nF.
How much did you increase R2? Another way to lower the gain of the BIG channel is to increase R11. If you go more than about 2.2K, you'll need to increase R8. The voltage on Q1-C should be approx 4.5V.
Have you tried tweaking the trimpots for best sound?