I think what you’ve done is admirable: auditioned with and without the nDAC and carefully analysed the results. It seems like you’re doubtful about adding the nDAC. Others may well have different experiences, but it’s your ears, your room, your musical tastes, so I’d go with your own findings.
BTW I found exactly the same as you when I compared a Chord Indigo with DC1 (fed from CD5XS). I am sure others will disagree!
Roger
I think maybe this is only audible with an extremely high-end equipment
I am now listening again to the bare ND5XS2 and I certainly notice there are differences but in my opinion the differences are really too small to justify spending €1000 on the nDAC.
The tempo of the music sounds a tad faster with the ND5 and the nDAC seems to portray everything SLIGHTLY relaxer. Maybe my perception is incorrect and maybe that part is called “better timing”. But I love it when a rock track plays as if the tempo is higher (as if is sped up with 5%) cause it gives the music so much drive and energy. With the nDAC it seems it sounds slower and therefor with less energy.
I think focusing on hifi (sound etc) to much can make us miss the shifts, coherence and musicality of a better source. Better sources can often seem more relaxed, but really the musicality, shifts in timing and coherence is portrayed better and in prolonged listening makes more musical sense.
I have lived with the ndac for a long time and it is quite dark, natural and the bass is really full, yet powerful and musical. If I were you I would give it more time listening and focus more on music, like peaces you enjoy and see how you are drawn into the music over time. Do not shift back and forth to fast and dissect the sound. Give it some time and see what happens when you listen to different genres. Just some thoughts on testing, and sound vs music.
Good luck
F
Well said @Fred11. I can listen for hours on end with my nDAC no fatigue at all. Highs just seem so damn natural. I’ve heard adding a PS is the way to go, but I’m in no rush. Maybe ignorance is bliss. haha
Assuming you have bought the nDAC I would listen to your system with it in-situ for a month or so, then remove it. After a week you’ll know whether you can live without it.
I find your comment about relaxation interesting. Good digital allows ME to relax, could this be what you are experiencing, rather than any change in tempo.
I found a definite uptick when I added an XPS to my nDAC, all those years ago! Of course, the whole hog is a PS555 (non-DR I believe).
M
Seconded…
(It’s certainly cheaper)
I didn’t buy it. I have it on home demo.
With sounds relaxer I mean it is as if the music plays at a a slightly lower speed. I would describe it as if the speed of the ND5XS2 is normal speed then the nDac sounds as if the music is slowed down 2% or something.
I think indeed that dark is the word that describes it well. I think the DAC is darker than the ND5XS2 and maybe that’s the part that I am experiencing when describing the clarity.
Good point on the testing advice.
“Dark” is certainly the word I have used to describe the difference between the nDAC and, for example, my CDX, and indeed the Musical Fidelity V-DAC2/V-PSU that the nDAC replaced.
At first I wasn’t sure that I liked it, and I reported as such on an earlier thread.
But with an nDAC and XPS, the upgrade cost is getting to NDX2 level so that really needs to be brought into the comparison.
Roger
that’s three vs one box and actually costs more than a NDX2
The answer to the question ‘how do I make it sound better’ is always ‘add another box’… 
“Slowness” effect could mean that you are hearing ripple effect near cut-off frequency introduced by digital filter implemented in nDac. In a good revealing system this is entirely possible.
I would love to know what that means haha.
Poorly mastered source may contain “illegal” frequencies above Nyquist frequency (half the sample rate), if you pass that to a bandlimiting filter typically implemented in digital chain of a dac (or prior to it), it causes so called ringing artefacts - signal is overcorrected at transition points. Audibly these are “echos” near transients, especially noticeable as pre-echos.
But don’t take my word on that, try different recordings, the ones you can trust are well mastered should not cause such effect.
Naim DAC plus 555PS plus ND streamer? Plus three levels of Fraim?? Plus a PowerLine or three?? Madness, surely!
(Ermm . . . guilty, m’lord. 
)
If I remember correct most other high end dacs and amps is much more wideband than Naim just due to that problem. So why would naim chose this design if the problem can be removed?
It is one of those “pick your poison” situations - designing a filter is an act of finding acceptable balance between different trade-offs. Do you accept high-frequency roll-off, let some aliasing distortion pass through, introduce phase-shifting or live with ringing. Only your ears can tell what sounds best in your setup and with your senses.
Hi Roger,
Very true. I would see this as a buying on a budget exercise, for which there are a few options.
M