I had a Nova (I loved that thing) and while planing an upgrade, I demoed a SN3/Chord Qutest or Hugo 2 (don’t remember). The difference wasn’t huge to my ears with B&W speakers.
I tried a SN3/NDX 2 vs Nova and the difference wasn’t very important (to my ears). The only time when the NDX2 shined and outperformed the other combinaisons was when it was connected to another amp (non-Naim amp).
I think the Nova is a wonderful all-in-one (even when compared to more expensive systems). It can please a majority of listeners when paired with the right speakers. So my modest advise : keep the Nova, it’s hard to beat if you are not planing to invest a lot more.
We still have the Nova, it’s lovely and isn’t going anywhere. For the main system, it’s been through a few iterations now, starting at the NDX2/SN3 and now a NDX2/555PS/552/300. The NDX2 is one box that can take you through many upgrades, so is a pretty solid choice. With the amplification, it’s just a case of how far do you want to go, and then try and take as few steps as possible to get there. Always enjoy the music first and the journey second.