BA3121: Ground loop supression is great however very thin audio quality
The schematic is not complete. There is no source of DC_bias for pin_2, pin_6.

As an aside, I'd increase the size of the caps on pin_2 or pin_5, by 5:1, so the HPF high-pass-filter behavior of the biasing drops by 2 octaves.

Perform some causal exploring.