Most musical, enjoyable affordable amplifier

On digital ,it is the Lumin D-1,that Foes Tidal, MQA,Roon, with the excellent Mojo audio seperate 12v power supply 12lbs  still early 6am .
Gato Audio Integrated class D but stacked with technologies
I HAVE THE 400s 40wpc,800 In to 4ohms .Architecture looks great also.
Natural warmth ,and iron grip .over 20 design upgrades in the New S model 
Not cheap but will compete no problem with any competing brands.and the digital Section is very well balanced .

The most enjoyable listening , out of scores of amps, tube and ss, I have ever enjoyed, is the humble little Dynaco ST-35 with Mullard el-84's, and a Pass First Watt F6 clone  built from Pass article ,and DIY Audio web site.
Class A does it for me.

One of my favorite amps was the little PSE Studio IV. Compared to just about any other amp near it's price, whether driving my Vandi 2Cs or Quads, it was like pulling back a veil and just hearing the music...Jim

I bought a modern single ended tube "boutique" guitar amp (I'd owned old Fender amps, some of which were single ended) and liked it a lot, and it got me wondering what single ended tube hifi would sound like after many SS amps over decades, although at the time I was enjoying a push-pull tube power amp in the rig. I read about Dennis Had and watched an interview with him on Youtube that I liked, and a slightly used Firebottle amp showed up on Ebay. After a year or so I'm still smitten, and while using it with efficient speakers and a tube preamp it simply works for me as it sounds astonishingly good. Seems to be a keeper.