Folks here created PCBs with Chuck's mod
R11 - 1.5K
R12 - 5.6K
C5 - 1uF
C6 - 220nF
I made szukalkis speedysheep with that switchable mod. The C6 really changed the mids and fattened it. So you better should stay with the 100nF.
Best bet would be to breadboard it and check out for yourself.