I have a Calypso tube preamp. It has fully balanced differential inputs and outputs. When I use the differential inputs and outputs I loose much of the tube character of my preamp. I have a tube preamp to get the euphonic tube sound to music. Tubes improve the emotional impact and add a wonderful organic character to the music. The differential inputs and outputs seem to be clearer and possibly more technically accurate versus the single ended ones. I guess that is due to the noise and distortion canceling effect of true differential circuitry. I use the single ended inputs for music and use the differential inputs for HT. I gather this only applies with true differential circuits and probably wont apply to Macintosh. If so, then I would think the XLR connections would be best whenever they are available. Of course, the only true answer is your own ears. This is just a guide to know what kind of things to listen for.
Bob
Bob