Is a single 20 amp dedicated circuit enough to run mono blocks

Never seen those, looking at the manual from Bystron they consume 1100 watts, your breaker should be just fine. Looks like they come with a breaker built into the switch, doesn’t say any rating. BTW, bet they’re going to be some outstanding amps.
http://www.bryston.com/PDF/Manuals/7B3_Manual.pdf