@lanx0003 I have not listened to the Apollon but I had given it some research. Just on looks & the couple extra features & upgrades I would have preferred that model. But I really didn't need a new amp..was just curious about the newer Nilai tech & power supply. The Stereo DIY was the cheapest I could find & I figured worst case scenario (no difference from Ncore) I could resell it with minor loss. Basically I wanted a taste of the newer tech at cheapest price. Personally I like the look of the Apollon.
Now that I know firsthand about the Nilai I at least wish I would have gone for the mono blocks. Although I certainly don't "need" them for extra power.
Definitely there are ways to change the sound of these amps with whatever op amp or buffer. There are quite a few selections to choose from depending on the company. Problem is..which one or ones sound best? Is there a popular opinion on which one is subjectively "best"?
Going back to the Elac class D amp I mentioned the input stage made all the difference. I had heard the basic Ucd modules but Elac did a Jfet or Class A input driver that took that mediocre module to a new level imo.
I while back when I was looking at different amps I liked the idea of the VTV tube buffer but it seemed a little pricey & I don't recall seeing any specs for it. My opinion was I'd be better off going with a tube preamp then an add on tube buffer. Which I'm a big fan of pairing Tube pre's with Class D...or really any amp lol. I've experimented with a few different pairings. Tube pre with low power supply noise & a smidge low harmonic distortion sounds good to my ears. I just started & almost finished with a new preamp build to pair with the Nilai. Minimal circuit design & the designer provides specs. Small parts list so upgrading to V-caps, mundorfs, AMRG carbon films & such wasn't too bad.