If you really want to have a tone control, what you want to do is add a tonestack on the output. On the main site there's a layout for a big muff pi tonestack with a booster at the end. Simply take the output from the Blackcat and bring that to the input of the tonestack, then the output of the tonestack becomes the new output. There's a trimmer to adjust the output, and you want to set it so you have the same amount of output you have without the tonestack there.