John Ulrich died in 2015 but is consistently regarded as a magician with his amplifiers. The hegel 390 is a beautiful piece of work as well, and has newer technology in it. I’ve heard the Michi driving some somewhat underwhelming Martin Logan’s so I’m not sure whether what I heard was underwhelming because the speakers or because of the amp.
Your viennas are four ohms and a rated at 89 DB’s so you don’t want anything too high-powered. I mean, most amps don’t run it anything near full output, but I would say 200 watts at the very top for your speakers. Anything more than that I think is going to be a waste of wattage and price.