This really would be easier with a bipolar supply.
Single supply with lifted reference is simple for simple circuits. Here you are going in and out a LOT, forcing many-many in/out coupling networks. You drown in R-C parts.
The coupling between IC2A and the switches is not needed. (I ass-ume the switchs are never both open.)
The output to SND must be DC blocked,
Likewise the input at RET.
The output really does need some ground return to protect against truly floating connections. In the most likely case of hard-bonded grounds at slightly different potential, the resistor does not add to ground-loop area.
The output, as you say, needs two caps. The shell reference cap must be quite large; not 70.7% (3db) at 82Hz, but well under 10% reactance at 50/60Hz.
The 47K resistors must be better than 10% match; use 2%.
The VR must be fairly low impedance.