HELP with bass boost to plexi PEDAL

[reubster]

I want to increase the bass response or "Push" of this pedal.

I have a basic understanding of Reactances, Filter circuits, Op amps and Clipping circuits but sometimes I find myself going around in circles and get confused.... :scratch
So I'm looking for so suggestions of where to start...schematic is attached below...mine is later version so ignore red values

Here's what I think:

C9 [33n] & R3 [47K] form a Hi Pass filter [102Hz]...I could increase C9 to lower the roll off freq but this won't achieve what I want as it will not actually boost the amplitude of the bass for a guitar signal.

The non-inverting gain of stage 2 is set by RF/Rin + 1 [I am ignoring the clipping effects of LEDs]
Assume RF is set to 100K
We can calculate Rin by adding R4 [47 Ohms] with the Reactance of C11 [2.2uF] at a given frequency.
So increasing C11 will decrease XC and thus increase the gain...This will have greater effect at lower frequencies
This is probably what I need to do and it would be easy to switch another cap in parallel with C11.

There may be something else I can do with R6 & C12 and/or the tone circuit: but I'm not confident I have it nutted out right...basically use R6 [4.7K] as Rin and the parallel combination of R7[22K] and [Tone pot + Xc of C13] for RF.
To my ears it sounds like its a treble cut cct and the bass is unaffected, so it probably won't help me anyway as I want to increase the bass with respect to everything else.

I realise it would probably be quicker to just try this out but I like to understand the maths behind it.
Your comments will be greatly appreciated.

http://img368.imageshack.us/img368/2...unarev3jd5.gif