The Bryston ST lineup is a little hard and can be fatiguing, though with a tube preamp you should be good. I have owned the 3B-ST, 4B-ST, PowerPac 300, and 7B-SST,
The following upgrade program is something to consider even if the 7B-ST is a backup in the future.
(11) Here's how BRYSTON makes OLD amplifiers NEW again! - YouTube
The ML amps I have heard sounded pretty good, not fatiguing, but not the clearest sounding (a bit dark for me). At one time I was thinking of getting the ML585 integrated. Today, I prefer Benchmark AHB2, CODA #8 and #16, and the new KRELL XD amps. I am saving up for a new XD amp (sold 2 lower powered ones)..
BTW - USAM has 2 KRELL Duo 300XD amps for a very good price. Not sure if it would pair well with the ARC preamp, but I am certain is it better than the ML436 (to my ears).