Another two cents: Of all the amps the OP mentioned, the only one I've ever spent any serious seat-time with (i.e. approximately 2 hours) when I was auditioning for a two-channel system speaker upgrade several years ago was the MF m6si. That is one fantastic amp, provided it is matched to the right speakers. I listened to it with a couple models of Paradigm towers. Forget the model numbers but they were in the 3K and 4K price points.
Integrated Amps
I'm debating whether to upgrade my Marantz integrated with a better performing and higher powered integrated or simply add a separate amp and use the Marantz as a pre-amp. I've looked at stepping up to the Marantz model 30 or 40n, PS Audio Stellar Strata, Music Fidelity M5si/M6si. But then the Heaven 11 Billie caught my eye.
Has anyone had any experience with the Heaven 11 Billie integrated amp? It's a hybrid class D amp w/ a tubed pre-amp. The reviews I've watched seem to give the unit high marks for sound quality, presentation, sound stage, and because of the tubed pre-amp, an analog warmth to the otherwise "cold" sound of a class D amp.
https://heaven11audio.com/billie2-amp-features-specs/?v=7516fd43adaa