Some may remember me posting about frying my Quattro when I carelessly inserted an op amp the wrong way around. We also discussed the design of the Quattro and what the benefits (or options) might be for rolling op amps.
The following is advice direct from Matrix, but please note they do not recommend or support the changing of op amps as you will instantly void your warranty (like me!)
But please note: After replacing the op-amp must re-adjust the headphone output direct current, adjusting the potentiometer (near four op-amp OPA604), 4 measurement point voltage adjustment to ±0 mv, as small as possible, otherwise, the direct current may damage the headphone.
measure point1： the pad in the middle of R49 and R50
measure point2： the pad in the middle of R53 and R54
measure point3： the pad in the middle of R51 and R52
measure point4： the pad in the middle of R55 and R56
What they're referring to here is adjusting 4 little screws inside the amp which regulate the power output to your headphones. I'll take a pic when my amp is back home to make it clearer.