When you convert from singled ended to balanced out(using a non balanced circuit topology), depending on which method is employed by the manufacturer, it is possible that it could lead to inferior sound with the use of that connection. In the example of the Sony, most will agree the SCD-1 does not sound as good through its XLR out but better through the RCA's. Part of this can be blamed on the way Sony has executed this specific output conversion.
Using XLR for simply lowering noise levels in such short runs of cable(1 meter or so) is questionable and unless it was in an awfully poluted enviroment, probably wouldn't accomplish much in absolute terms. This is exactly why I think some have said they received better sound from RCA connections (and I don't doubt it.)
Simply terminating equipment for the sake of having XLR's is questionable in my opinion unless longer runs of cable are implemented where some advantage could possibly be obtained. The conversion process does run the probability of some sonic degradation just as adding anything extra into a circuit(such as even an additional solder connection.)
In talking with Ayre and a few others, genuine balanced circuitry is improved with XLR's. Ayre uses what is the equivalent of 4 amplifiers in the V5x. Each channel uses a mirror imaged pair of amplifiers. Each side of the balanced connector is fed to one amp. One amps output is connected to positive, the other to negative speaker terminal. One amp produces half of the wave, the other the other half since in actuality there is no + or - on AC output, only phase difference. (Speaker terminals are labeled + or - so they may be oriented with the other channel so both are in the same electrical phase relationship) There is no chassis ground for the interconnects either single ended or XLR.
Mixing down the two channels via single ended would degrade the sound and Ayre indicates this. It certainly isn't hard to hear on my part.
At any rate, I suppose each person, with their associated equipment, must decide if it is worthwhile. What I have stated above is why I think there's so much variability on this subject.
