I am glad that your W4S ST500 can drive your new 645s!
Just like you, I am also looking for a second ‘summer amplifier’.
What do you think is a top tier Class D amp?
I would like to read more of your listening impressions regarding MA1s vs. ST500.
P.S.: I am considering this ‘top tier’ Wyred4Sound. Unfortunately no dealers in Vienna 🙁