I'd like to hear someone tell us how Atma Sphere amplifiers are anything BUT reliable. Personally, I haven't come across a more reliable amplifier, be it Class A, Class A+, Class A/B, Class B, Class D, or Class XYZ.
Yes, if you want heat, a Class A amplifier is your ticket. Nice in the winter. The power draw isn't a positive, but that's about it when it comes to drawbacks. I concur that Class A often goes hand in hand with great sound. The Atmas being as good a Class A amplifier as you'll ever come across, particularly if tubes are your cup of tea.
Never understood those who were running their Atmas in Class A/B mode. As I like to say, "In for a penny, in for a pound." In my opinion, you run your Atmas the way they are supposed to be run, with the kind of speaker they are supposed to be mated with, or you find some other amplifier.