That's correct, the subs are connected with RCA to the M33 pre outputs. Not sure Roon can indeed delay the speakers without affecting the subs but then again, 2.5ms is not that significant. I am waiting to learn more about M66, that can manage subwoofers in time domain, before deciding is an upgrade is worth it. While M66 has the same price as M33, I'd need to buy the M23 or another good power amp to make the system work. Active speakers to beat my 2446/2500 Heritage Specials are really expensive, but that's also an option to keep the system to a one box solution.