I/V conversion connect to Tube buffer in.
Face to the PCB, please find R19 resistor (2K)
The left hand side of the leg is the I/V output of Left channel,
connect it to tube buffer left channel input
Find R21 resistor (2K)
Left hand side of the leg is the right output.
The GND signal (typical is a shielding wire)
Connect L GND wire near C45 GND position
Connect R GND wire near C55 GND position.
Hope can help you, any question, please email to me.
KK
kk_ho@hififever.com