Metronet, you can conduct a valid comparison of Bel Canto Ref 1000 Mk.2 against one particular class A amp, but a generic comparison of a single class D amp against the entire class A group is not possible. . . there are enormous differences between individual amps in any particular class, and there are sonic overlaps between classes. It is likely that you would find Ref 1000 Mk.2 more pleasing than some class A amps, and less pleasing than other ones. .
I have not listened to the Accuphase A-20 amp, but I have reviewed the Bel Canto Ref 1000 Mk.2 for Positive Feedback. See:
http://www.positive-feedback.com/Issue43/bel_canto_ref1000.htm
Hope this helps, Guido