art Tube Pre M3 sch.pdf
Not this exact unit, from what I can tell, but the only one I've found around the net.
Looking at this schem, I see unbalanced outputs only use half the U2 chip. I'll see what difference I get using balanced outputs.
Also the phase switch is between the final buffer and the outputs. I'll massage that as well.
Still thinking that it's an output impedance issue. Am I right in thinking that I can load down the outputs to detect if one channel is failing to deliver sufficient current?
I'll see what difference I get using balanced outputs. No difference.
I'll massage the phase switch as well. No difference. Sigh.