I can't answer too much of what you asked, but I'd suggest wait till the speakers come in and see how they sound with the Adcom, then go from there. The newer model may be an easier load than the old Sovereigns. I know of people on this site who drive Dunlavy SC-Vs (the next generation of John Dunlavy's design that most closely equates to the Sovereign) with the 100wpc Aloia amp with great success, so don't get all hung up on power, the Theta would probably work well. You could also ask the folks at Duntech what they'd suggest (I wouldn't be surprised to hear Plinius mentioned; after all, they are Australian) for some ideas as well.