Just an observation.
These days the Baxandall feedback tone control is almost universal in audio reproduction amps, ghetto blasters and so on, but it is not one that is generally favored by guitarists in music creation amps, I suspect because its operation is radically different from most other tone controls, particularly the ones favored by guitarists.
Most guitarists seem to favor a bit of "mid-band scoop" (which sounds like what you are seeking) and this matches up well to the majority of controls that have a "hinge" around some mid band frequency (typically 1kHz for reproduction amps and 440Hz for creation amps such as guitar amps).
These generally operate by introducing an adjustable slope, rising or falling, from the fixed hinge, with the slope set by the control.
The Baxandall doesn't operate like that at all. It introduces a fixed slope which "slides in" from high and low frequencies, the control setting how far the fixed slope is between the frequency extremes and the mid range, effectively an adjustable hinge. To get mid band scoop with a 2-band Baxandall generally requires very large values of boost or cut at the frequency extremes, and this is not what guitarists want.
Although it doesn't include Baxandall, if you haven't come across Duncan's Tone Stack Calculator I suggest that you download it and have a play.
Introducing a mid control element may get you close to what you are looking for, but you need to be careful to select a mid frequency of operation where you want your scoop to be centered, that is closer to 440Hz than 1Khz where most designs will be set.
