So I switched from XLR cables...

Better designed balanced cables sound better when used with a truly balanced system, period. When I have the choice I always go for balanced. Otherwise, if you must use single ended (like with my Dennis Had Firebottle amp which has only single ended inputs) ICs they also sound fine of course, if you stay within the run length limits. 

balanced signals require both halves of the signal propagation to be exact and then electromagnetically and in voltage fields..interact and reflect off/in one another in perfect symmetry of their perfect signals.

Nice theory.

Reality says it has it’s limits.

It gets niggling little bits of it wrong. It is not possible to make it perfect enough for the theory to emerge as a reality. *

Problem being that it’s distortion components are the parts that the human ear uses for fine levels of discernment...

....which is the whole high end audio pursuit itself.

Both balanced and single ended RCA.... both being imperfect...as well as the rest of the system and the humans being imperfect (different hearing, different mind, etc)..combined with how the human ego/limits function in the meat box we call a human...those things all combine into, or emerge as - arguments among the meat boxes.

~~~~

* The Teo audio liquid metal has the ability to deal with physical perturbations and inconsistencies in construction..whereas frozen lattices of solid wire, due to how signal propagates in it..cannot. In this.. the problem with wire in balanced design..is pretty well wholly eliminated with the Teo Audio liquid metal conductor pathways. This point is utterly unique in electrical conductor design.

Great Captain, the Parasound conforms to the AES standard. Now how ’bout the Mac?

From manual:

Balanced XLR Input Jacks
In most systems balanced XLR connections will give you the best sound. If your stereo preamplifier has balanced XLR output jacks, we recommend that you connect them to the A 21+ XLR inputs. Refer to the Balanced and Unbalanced Lines in the Technically Speaking section for additional information about why we recommend using balanced lines.

Note: Using balanced XLR input connectors results in a 6 dB higher volume level compared with using the RCA input jacks. This is a noticeable increase.

Unbalanced RCA Input Jacks
Use these inputs if your preamplifier doesn’t have balanced XLR output connections or if you simply prefer to use unbalanced connections.

Balanced/Unbalanced Selector Switch
Place the switch in the position for the input type you will be using.

Note: The Balanced/Unbalanced switch is not an input selector. Its function is to optimize the signal to noise ratio for each type of input. You should not connect both the Balanced and Unbalanced jacks at the same time with the expectation of switching between two different devices such as a preamp and surround processor.

Balanced XLR Pin Configuration

The A 21+ XLR jacks conform to the industry standard of:
Pin 1: Ground Pin 2: Positive (+) Pin 3: Negative (–).

I'd like to introduce a new thought in addition to almarg's comments..  Even though capbeaver's XLR and RCA cables were made by same manufacture, there could be a significant difference between them.  Are the XLR/RCA cables the exact same model?  Or different models.  Maybe the XLR is silver/silver-plated wire and the RCA is copper?  Are the XLR silver-plated?  Maybe the RCA plugs are gold-plated (which would be a much warmer sound than the silver plated).  Also, many cable brands use a basic Neutrik XLR plug.  This can have a slightly dry/harsh sound because they use hollow/thin conductors.  The RCA plug could have a solid center-pin and conductor element, which could dampen the electrical resonance that shows up in the low mass Neutrik XLR.

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

Comments WRT Prior posts above

(A) ....Mac 41 pre into new A21 Parasound ... balanced to balanced...I’m a tweeker so more to come BUT the rca’s smoked the xlr....

(B) ....XLR sounds better than RCA in my system. If your system isn’t fully balanced XLR may not work for you. .

MY TAKE: the differing opinions support my experiences that it is ENTIRELY system dependent ..,,full stop.

Why?

(1) A mag review of that PARASOUND amp states that it is not advised to use both the balanced and unbalanced inputs at the same time, which is cumbersome ( at a minimum...) in many systems. The new Parasound Halo P6 preamp was recommended as a proper stablemate to solve this issue. I don’t own it, but my read is that possibly mixing them up with mixed brands might introduce some compromises.

(2) Some systems manuals DIRECTLY suggest the mfg. XLR preferred pathway to audio OZ. For example, my REGA OSIRIS integrated amp and its stablemate REGA VALVE ISIS cdp/DAC manuals (and dealers ...) both specifically recommend using balanced interconnects instead of RCAs. In a length comparative shootout of ICs in > $1000 range,

(I) both the dealer and OEM manual recommendations were confirmed to me in spades.
(Ii) the actual selection of cables also do matter. NORDOST FREY XLRs bested all the half dozen plus contenders and pretenders in the $1000 - $1500 price point strata in my system. As a side note, all the brands bested the $200-$700 options fwiw.

Parasound amps are NOT balanced, they use IC conversions on the inputs. The JC1 or JC5 might be different but generally most of them are not differential balanced.

@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.

Mac 41 pre into new A21 Parasound ... balanced to balanced

im a tweeker so more to come BUT the rca’s smoked the xlr

Hi,
if your equipment is balanced from input to output then XLR will most probably sound better, as it will have less noise and more dynamics. 
XLR connection does not translate to fully balanced design.

XLR sounds better than RCA  in my system.  If your system isn’t fully balanced XLR may not work for you. 

XLR is designed for professional use where cable runs can be very long and a lot of stuff is being connected and disconnected so the locking feature is essential. One of the first decisions I made long ago was to figure out XLR is unnecessary for home use. Beyond unnecessary, it doesn't even sound as good. As you just learned for yourself.