Hi dayglow, will, I just noticed your question months later, sorry about that!
About the Norma Audio Revo IPA-140 and your questions:
I would say that the XLR input on the norma is there for convenience. But it is true that input 4 is THE input with the optimal sound. The other inputs (including the XLR) are very good also, but input 4 is the one configured with apparently the shortest signal path and whatever else they configured. Difference isn’t great between that special input 4 and the others, you have to really listen for differences. But to call the other inputs "compromised" is a stretch in my opinion.
I happen to own XLR Ref3 cabling, both XLR and RCA, so I was glad I could still use the XLR and able to make direct comparisons.
Can’t tell you how good the sound of the preamp is because it never occured to me to think of the front end this way, but the whole is pretty magical. One thing for sure, the sound is not veiled in any way, you hear EVERYTHING.
Strongest attributes about this amp (highly subjective of course):
1. Absolute neutrality, if there’s a bass-boost in the recording you will hear it. And voices are done exceptionnaly well.
2. Resolution. Again, if there is the slightest detail at the back of the soundstage, you will hear it.
3. The whole clean, minimalist concept. It is the type of product that when you get very close to it, build quality is superlative, as it should be given the units price.
4. I am not knocking companies that assemble partly or wholly their gear in Asia (I did own a previous Ayon Orion which sounded great) but there is something about having gear that is hand made in Italy. And I am biased to Italian amplifiers, what can I say, they almost ALL do voices right regardless of manufacturer.
5. I have the optional USB DAC card (in two separate parts) installed. For what it is worth, it surpasses by a long run the Sabre dac inside my Oppo 105. Even though the Norma dac sounds better, I most always use the Oppo dac for convenience (and it does sound nice) as I can plug USB hard disk right into it, and keep the norma dac for when I wish to connect my Apple laptop occasionnaly. But again, the norma dac is superior to my ears, and the increase in quality is pretty easily heard.
What I like less about the norma revo IPA-140:
1. Even though I love the minimalist design, my particular situation would now require an additional set of speaker outputs. Also, aside from being able to transform inputs into outputs, there are very few features on the amp. Sometimes I would welcome a mono switch, but that’s about it.
2. I wish I didn’t have to keep pressing the button to go forward through every input to go from (for example) input 3 to input 2. However the remote can go back and forth on input selection no problem.
It is an exquisite integrated on all counts.
Hope this helps,