First Foray into XLR

Switching the VAC to XLR was mind blowing. We switched back and forth...

Unless the output signal is verified within 0.1db across the whole spectrum, back and forth switching is rather pointless.

If the cables are not identical, then cable deltas could swamp the electronic.

Different connectors of the same type with identical cables can be audible.

Uncontrolled variables have been skewing results since time immemorial.

@ieales We did not simply do A/B switching (I am not a fan of simple A/B switching). We extensively listened to both amps and to the VAC in both RCA and XLR inputs, at various volumes, and assorted genres of music, experimenting with two different, quality RCA ICs - a .5m pair of CablePlex Silvers and a 1m set of low capt. high res 99.9% copper. The result (even when compensating for volume) was consistently, a wider, deeper stage, with more air around individual vocals and instruments, when the Vac was running through it’s balanced circuit.
With your logic, nothing is, or sounds, any different than anything else - it’s just a matter of volume.
Even when adjusting for volume, we did not expect to hear an improvement on the VAC’s already incredible performance, but we did...Jim

I don’t doubt differences were heard.

when compensating for volume

Since you adjusted volume, then you concur that matching volume has merit. Exactly how did you compensate?

With your logic, nothing is, or sounds, any different than anything else - it’s just a matter of volume

Not so. I did not say that. Never have, never will.

I’m not trying to be obtuse, but I’ve endured far too many "night and day" / "blows the doors off" claims only to find that levels were not matched and when they were, deltas diminished drastically.

No mention is made of the driving device.

The effects ascribed to the XLR input could be impedance mis-matching. The VAC Phi200 does not list bal/unbal impedances.

The Phi200 manual states there are switches for bal/unbal. What was the power setup and is there a possibility of a ground loop with the unbalanced that is mitigated in the balanced mode?

When properly implemented, there should be extremely little difference between balanced and unbalanced at home HiFi distances. I spent a couple of decades designing electronics [not power amps] and made sure there were none.

@ieales
Looking back, I've got to laugh a bit at my own statement, as mind blowing and blows away aren't terms I usually use when describing, what are usually quite subtle differences, when comparing A and B, very nice components. I would not say that the difference was mind blowing, just the fact that it could possibly sound any better than it already did, along with the overall engagement of the performance.
As far as the driving device - not really sure which of John's collection of players and DACs he was using, certainly one far and above anything I have. Our original quest was to compare the The PrimaLuna to the Vac. We did not switch around any components - other than the two amps and cables, along with a bit of tub rolling with the PrimaLuna.
All of my equipment is single ended and in all, have been quite happy with what I have, including my silver RCAs...Jim

The first thing to be skeptical of is manufacturers who install XLR I/Os, but their component/s ae not balanced internally. How is one to tell anything in tht case? 

Reviewers who are tasked with reviewing actual XLR kit seldom have differentially balanced systems. How many times have I read them say "I hear no difference" Meaning Editors should be shot, then hanged, then shot again for such stupidity, and yet, it has gne on this way fo decades. I used to send nasty letters to such editors, but finally gave up. You can't fi stupid.