200K is way too high. The impedance will be too high to overcome cable
capacitance and electric noise. 1K would be more like it.

No, 1kohm would be worthless. It would provide somewhere on the order of
0.2dB attenuation, which would be inaudible.

I suggested 200k ohm as a POT value, so that he has sufficient range to make
the determination. I suspect the resistance value that will provide the
results he's after won't exceed ~50kohm.