bdp24 6-17-2019
@captbeaver, have you verified that both the Mac and the Parasound (and your XLR cables) are wired in accordance with AES File 48? That is, Pin 1 is Ground, Pin 2 is Non-Inverted Signal, Pin 3 is Inverted Signal. As Ralph Karsten of Atma-Sphere has stated here dozens of times, it is only when all XLR connections are wired in accordance that you hear the benefits provided by true balanced signal transmission.
@bdp24
Eric, to be sure it’s clear there are several major technical criteria Ralph has cited that must be met for the potential benefits of a balanced interconnection to be realized, and the pinouts that are used are the least of them. And in fact most equipment that is manufactured in the USA or is intended for USA consumption conforms to the pinouts you stated. And in cases where it doesn’t conform the only consequence is that pins 2 and 3 are interchanged, which will result in a polarity reversal but will not affect whether or not the benefits of balanced interconnection are realized.
For Ralph’s comments in that regard, in which he indicates that the majority of consumer-oriented audio components which provide balanced interfaces do not meet the criteria that are necessary to realize the benefits a balanced interface can potentially provide (including even many components that are "fully balanced"), see his first post dated 3-22-2013 in this thread. Also see my follow-up question later in that thread, and Ralph’s response.
Regarding the OP’s finding, I agree with akg_ca that it is entirely system dependent. When the cable is changed from RCA to XLR or vice-versa, not only is the cable being changed, but the configuration of the interface circuits that are being used in the two interconnected components is being changed; susceptibility to ground loop effects is being changed (which will depend on factors that are often unknown such as the internal grounding configurations of the two components, and on whether each component connects the shields of the cables to circuit ground or to chassis, and on how circuit ground and chassis are interconnected in each component); in many cases output and input impedances may be changed; and speaking more generally the basic operating principles of the interface are being changed. None of that has anything to do with whether or not the internal signal paths of the two components are balanced (i.e., if the components are "fully balanced"), and a lot of that doesn’t have much if any relation to the lengths of the cables either.
That said, though, anecdotal evidence does seem to indicate that more often than not an RCA interconnection will be preferable to an XLR interconnection if the components do not have balanced internal signal paths. The likely reason in many cases, as stated earlier in the thread, being the use of inexpensive IC (integrated circuit) op amps to generate one of the two signals in a balanced pair of output signals, or to convert a pair of balanced signals that are being received to single-ended.
Best,
-- Al