Best way to connect balanced audio line to ADC (with volume pot)?
Does anyone have any idea which way I should go here?


Consider initially the 3 op-amp amp Instrumentation Amplifier (InAmp): -



Gain is set by one resistor (\$R_{gain}\$) and, if you throw away the final stage op-amp circuit and take your differential output directly from the two op-amps to the left you should get what you want. You do need to spend a little money making both R1's matched but maybe 0.1% devices at 50 cents isn't a biggy.

Differential leakage capacitances either side of \$R_{gain}\$ should ideally be zero for a perfect match but if you are only dealing with audio it won't be much of a problem.