it would depend on the brand
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there is not necessarily a difference in quality of the sonic presentation between an interconnect with RCA vs. XLR terminations. The only difference is that the XLRs will typically give you a 6db gain over the RCAs, so at the same volume level, the XLRs will sound louder. So the difference in sonics will depend from IC to IC based on material used in cable, cable design/geometry, cable shielding etc...Only way to tell is to try out various options in your system.
I know that everybody suggests when you do long runs (very long) you should be going balanced. Surely this isn't just to get that 6db of gain, isn't there more to it than just gain. Some manufacturers suggest that sound quality will be better when going balanced. Not disagreeing, just throwing that out there.
My Rowland class D amp has only XLR inputs (mature decision) so I cannot compare but from what I've heard balanced gives a little more air. There is another reason for using XLR different from the sound quality, It is an arrangement of connectors that don't allow to touch/be touched. It is very important in studios with hundreds of cables passing and real possibility of cable being yanked from its place but in my system it is only sonics I care about.
See the first page or two of this paper for an explanation of one of the fundamental disadvantages of unbalanced interconnections. He refers to this as "common impedance coupling" of inter-chassis noise currents with signal return currents, caused by the fact that both currents flow in common through the shields of unbalanced interconnects.
Of course, whether or not this is significant will vary depending on the system, and also on the ac power distribution scheme.
Note that he refers to high frequency "buzz" as well as low frequency hum, which may correlate with the subjective perception of background "blackness."
Keep in mind, though, that if common impedance coupling is not a problem in a particular setup, AND if the components are not "fully balanced" (i.e., they are unbalanced internally and only balanced at their interfaces), a balanced interface could actually sound worse than an unbalanced one. That is because of the possible sonic effects of the extra stage that is introduced into the signal path to convert from unbalanced to balanced, or vice versa.
Al - Thank you for the link. I believe that grounding shield at both ends is a mistake but there are some studies showing improvement with high frequency noise rejection.
One important thing they mentioned in the article is to NEVER defeat ground loops by disconnecting earth ground (third prong). Device that uses only 2 wires (hot and neutral) is designed differently with no metal parts exposed. Disconnecting third prong (very common advise on this forum) can lead to death.