People responding to this type of post need to understand the difference between "fully differentially balanced" topography of top-flight equipment and the XLR "balanced" outputs of lesser gear, which has single-ended topography that is converted to XLR at the output stage using inexpensive (and often sonically inferior) op-amps.
If your components are fully differentially balanced (like Krell, Ayre, Classe', Pass, BAT, etc), then the XLR cabling will make a very significant sonic difference as it is required to utilize the differentially balanced circuitry. This equipment is significantly better sonically when using the differentially balanced circuitry via XLR than the non-differential circuitry via RCA.
If your equipment's XLR outputs are merely "balanced" connections (more marketing hype than anything), no difference will be heard except that the XLR signal level will be boosted by +6db and, possibly, a reduction in noise is possible with XLR vs RCA on long interconnects runs.
Good luck and Merry Christmas!