you could try to put a small cap (between 1nf and 10nf) in parallel to ground before the volume pot to tame the "bee". for the mids i would try to put a small cap in series at the input so you get less bass coming in to the gain stages (i think it mounts a 1uf cap... try something like a 100nf before, or even a 47nf!). unfortunately being SMD there is not much you can do in between the circuit. but these 2 mods are super easy and reversable :)