Method 1
not guaranteed stability)
2* 1kohm resistors needed
Find the output resistor. Find the end that connects to the output, solder one end of the 1k resistor to that point.
Find the inverting input of the opamp (the corresponding channel). Connect the other end of the 1kohm resistor here.
Same for the other channel.
Method 2: (guaranteed stability)
220ohm resistors *2
1k resistors *2
560p capacitors *4
connect two of the capacitors together to one capacitor(like a 220p capacitor with a middle node)
Connect one end to the output of the 2134 opamp, the other end to the inverting input.
Connect one end of 220ohm resistor to the output end of output resistor described in method1. And the other end to the inverting input of the 2134 opamp.
Connect one end of 1kohm resistor to the middle point of the capacitors and the other end to the amplifier output.
Do the same for the other channel.
Now you have a composite amplifier with opa2134 and tpa6120a2 that has super low distortion and zero output impedance.
Extra: you can use opa1612 or opa2140 or opa2156 to replace the opa2134. There will be even lower distortion and very low output offset.