As Bart says, it’s about current delivery. The higher and faster delivery of the current basically controls the drivers in the speaker better - a faster push of the driver physically, which provides more cohesion that gives a cleaner and more dynamic sound. Which is why the 80W rating for a Nova, SN2 and a NAP250 doesn’t mean much on its own, as you go up that range you get far better current delivery and grip on the speakers, giving much better performance as you move up the range.
So, yes, the SN3 will drive the speakers better than the XS3.
A big front-end up them creates a wonderfully engaging lively presentation, as long as the room suits. It’s so important, and really ‘part of the system’.
I think that’s a great idea. You will get almost Supernait 3 performance for quite a bit less than the price of a new Nait XS3. It doesn’t appear that you need a phono input which is one of the main changes between the two in terms of features.
The only caveat is that at some point the amp will need servicing. Obviously a used unit brings you closer to that date so consider the logistics of that especially if you are not in the UK.
I’ve heard the ND5XS2 with a Supernait 2 and it acquitted itself very well. The ND5XS2 is rather a gem, I’ve heard it paired with an ‘inappropriate’ amp, i.e. one that should be far too good for it and I found it to remain very musical and engaging, far more so than I expected. It was a real eye opener as I’m strongly biased to source first usually.
I also just got this combo, even though I was pretty sure I’d get the Nova for my main system.
But after auditioning both, I couldn’t go ‘back’. Found a used ND5XS2 and the same dealer gave me a great offer for a new SN3 (which arrived this week) in exchange for my Rega Elex-R, which was clearly overwhelmed after I upgraded my speakers last year. It couldn’t handle the bass of the Dynaudio HS, which is astounding for the size of the box (not sealed though). The SN3 has an incredible grip on it, I also auditioned the Rega Aethos, also very capable, but went for SN3 because of sound signature (PRaT), phono input and possible upgrade path (like HiCap).
This is something that may not have been mentioned yet, but depending on your plans it also may be worth considering that the XS3 is more limited in terms of future upgrades.