resistor network and cap, good filtering help

[Gabriel]

I build the Attack-o-matic IV, from boscorelli. It's a kind of Slow Gear, but much better.

The circuit itself changes the tone of the clean signal, more bright. The last part of the circuit, is to de-emphasis that, through this network:



What i need to do, is to have the same tone when bypased, doing effected/bypass comparision.

How to achieve that in the best way? installing trimpots? variable capacitors?

Any help, i would appreciate.