Note the 4 pin XLR does not have a ground so use pin 1 from one of the XLR-3 pin connectors.
within +/-10mV is good enough when fully warmed up b.t.w. no need to adjust it within a few mV.
Just to confirm if I understood you correctly:
I have a XLR -> 2x 3,5mm jack headphone cable and the correct way to setup the measurement is to connect the black measurement cable of my multimeter to pin1 of a random 3-pin XLR Out on the back and to attach the other cable to the tips (L+/R+) and to the sleeves of the 3,5mm jacks (L-/R-) on the headphhone cable. Then I find the correct pot and bring it as close to 0 as possible. Correct?
edit...
So... I did that. Results:
L+ | 30mV (sleeve left channel on the hp cable) |
L- | -36 mV (tip left channel on the hp cable) |
R+ | 14mV (sleeve right channel on the hp cable) |
R- | -15mV (tip right channel on the hp cable) |
I was surprised that the L/R+ channels are actually connected to the sleeve of the 3,5mm jacks. Measurements were "open case". They will drift further apart, once the case is closed and more heat is involved.
These are the best case results when I turned the pots all the way in one direction until it "clicked" as you forecasted correctly.
@solderdude You have been a great help to me. MANY, MANY THANKS!