Just got the HD6XX in. Haven’t done any A/B testing, but I’m enjoying their sound tremendously already, even without “burn-in”. Unexpected benefit of open back headphones: you can hear yourself harmonizing when singing along. 
At $233 incl tax, it’s an easy decision to keep these: beautiful sound, distinct experience from the closed back Sony 1AM2, and not insanely expensive.
Of course this is a very different product than the AirPods Max (no ANC), but echoing what a reviewer wrote elsewhere: for dedicated listening sessions I don’t need the ANC, and for noisy environments where I do need ANC I don’t need top quality sound: AirPods pro are fine on the plane. Sonic happiness achieved. 
Edit: the word “D@mn!” has been heard with alarming frequency around @JoeS lately. These things sound effin amazing. Perfect fit for my rabbit ears. :vb-grin: