IMO the BASS and TREBLE controls are too coarse and the concept is flawed anyway. Never use 'em, wouldn't miss 'em.

I'd like to see something better, like a simple EQ with memories or something similar. The whole preamp as gain and switcher concept is actually getting pretty long in the tooth, but that's a whole different soapbox.

Along more useful lines, you can insert a signal processor between each preout and mainin and tweak away. The beauty of separates.