what is the difference between the different versions of the Audiopax88 amps?

looking at a set of these to run my Classic Audio T1.4 horns as they look like a good match- I notice there are a few different revisions and curious as to what they are and if worth upgrading from an earlier version-
Seems most folk run them with the Avantgarde but anyone use other speakers with them and any thought on tonality??- thks