This algo is real handy, and to make it even more useful for bass guitar would be the ability to adjust the bass shelving frequency.

400 Hz is too high, so I use the lower mid to shape the bass as well.

If the bass shelf was adjustable between maybe 40 and 400 Hz then both mid controls would be free to do mid type things, ala Darkglass B7K Ultra’s eq section. 

Actually, the same goes for the treble shelf; adjustable between 3 kHz and 10 kHz or thereabouts..

Cheers