The OPA2134 is a waste of time.
I'd try an LME49720 as a drop in replacement or
a pair of LME49990 on an adapter.
If you find you can't turn the volume up very much I would lower the gain.
If you lower the gain you can also reduce the value of the output resistor (R11, R111).
I would use a value of 120 ohms and add a switch to bypass it all together.
Replace C4/C104 with ELNA SILMIC II, 25v, as big a uF as will fit.
Replace C11 with something like a Nichicon VR , 35v, also as big as will fit.
Keep the Zener. You can still use the power supply you have.