Here's the schematic.
The 1st stage is unchanged from the original version except the BOOST switch is deleted. TIGHT is a low-cut with maximum cut (minimum bass) at full CW. This replaces the BASS control in the original version. Q2 is a unity gain buffer that prevents the TIGHT circuitry from loading Q1. The 2nd stage is unchanged from the previous version. U2 and surrounding parts form two active filters. I first tried a Baxandall tone stack. Because the Mojito is very mid-forward, I found I was only using the top half of rotation on the BASS & TREBLE knobs. So I switched over to the boost-only bass & treble filters shown below. Setting BASS & TREBLE to zero provides a flat freq response from the top of C11 to the output. BASS provides up to 12dB boost at 85Hz. TREBLE provides up to 12dB boost at 5KHz. The BASS & TREBLE filters were inspired by BOTTOM & TOP filters in the ROG Thunderbird.
View attachment 56465