I used a voltage divider calculator to determine that the voltage at the out jack will be 99.8% of the voltage at S8 when using the stated values for R38 and R39. However, when adding the consideration of the resistance of P3 in parallel with R37 (39K), that would add more resistance to the upper half of the voltage divider. The result would be a voltage even lower than the S8 voltage. If this would affect the taper of the P3 vol pot, I assume it would be very minor. I would think you could bypass R38 and R39 and take your output directly from S8. I have no idea what function is provided by the R38/R39 voltage divider. Most of the circuits I have seen do not use this at the end of the circuit. Do you have any ideas?