I own 2 class D amps and love the sound of both with either my Harbeth 30.1s or vintage KEF 103.2s (desktop system):
-- Wyred 4 Sound ST-500 stereo amp (250 WPC). I bought a used one based on a couple positive reviews and a number of positive user comments. I sounded great from the first note, at least as good as any trad SS amps I've had
-- More recently, I picked up a gently used pair of Bel Canto 600M monoblocks. Again, they sounded wonderful from note-1, even a bit more refined than the W4S.
Neither amp has any of that treble hardness people talk about. They both sound exactly right to me, tonally and dynamically.
BTW, I didn't have to deal with burn-in with either amp. But if I bought a new class D amp, I'd burn it in at least 400 -500 hours. Class D amps & DACs are often described as needing epic burn-ins (I certainly found that to be true of DACs).