First, my terminology may be a bit off, as I have only been playing for three months after a 20 year hiatus. So I may really mean fizz and sizzle when I say mud. But, I note that, for the best sound, I have selected about a 3db BOOST at 250HZ, so maybe this solidifies the mud? What I do know is that I am not a fan of Mesa's on-board eqs. If I understand correctly, they are "passive eq devices", which means they only cut various frequencies using caps, and have no artificial boost. Mesa does this to preserve the pure tube circuit tone. So, in other words, if we took all our eq knobs and sliders and set them to the max position, we would be getting pure unaltered amp tone. This manufacturing philosophy does not produce the tone I want, but putting a graphic eq (or similar device) in the FX is a quick and cheap fix. I used to use an outboard active tone control (though it was rotary, not slider) when I played through my former Mark III, even though it had a built-in graphic eq.
Second, I confess that I do not know what a Sonic Stomp is! I would appreciate info on it, such as a link or the like.