https://forum.headphones.com/t/mono...ifier-and-dac-with-thx-aaa-technology/2307/28
Andrew from THX instructions:
1. The unit has balanced inputs, and unbalanced inputs and outputs. You can use the balanced headphone output on the front as a balanced output.
Yup, set to 0dB gain. It is possible to rewire the rear XLR3 inputs as outputs if so inclined.
2. And with some warranty-voiding simple soldering, it should be pretty straightforward to modify the unit so the two XLR-3 "inputs" become balanced outputs wired internally to the XLR-4 headphone out and controlled by the volume dial. i.e. remove C67, C76, C79, C84 to disconnect XLR3's from the ADC. Then patch wire twisted pairs connecting the two XLR3's pins to XLR-4 pins as follows:
twisted pair 1
L+: XLR3 J2 pin 2 to XLR4 J10 pin 1
L-: XLR3 J2 pin 3 to XLR4 J10 pin 2
twisted pair 2
R+: XLR3 J4 pin 2 to XLR4 J10 pin 3
R-: XLR3 J4 pin 3 to XLR4 J10 pin 4
Each XLR-3 pin 1 is already tied to ground so you can leave that alone. This configuration is a bit better than using the XLR-4 balanced output since the cables will now have grounded shields, and the downstream device will now have shared ground with the 789 product.
/End.
Note: - find an electronics guy in your area to do this, it appears trivial.