I think it depends upon how you are implementing it. Are you wanting to use a single XLR for both channels, or a separate one for each channel? I don't see that the single XLR instead of TRS would be that much better except from a mechanical contact standpoint. It certainly won't be worse. A single XLR jack will need a bigger hole than the stock TRS jack, but it should fit the available chassis real estate. If a stereo amp has output transformers and the signal cold connection of the transformers is floating then there might be a real advantage in terms of reduced crosstalk if one used a separate XLR connection and cable for each driver of the headphones. But of course Crack is single ended, output transformerless, and the signal cold is at signal ground potential for both channels. So there's really only left hot, right hot and the common cold for connections. Wouldn't really matter if one used a single XLR or two, as the cold connections would still be common in the amp circuit.
