ATC Scm 19 V1 Upgrade or what?

The SCM40 will work fine in your room assuming have the time, patience and skills to properly set up speakers and listening position.

Jim Smith's Get Better Sound book is a great guide.

I would move up to the passive 40, a big improvement over the 19 (either version).

Yes, plenty of power, a great match.

The pro active 20 is roughly the same price as the passive 40. Since you already have ATC amplification, the 40 will give you more bass and plays louder. You don't have to deal with stands. Yes, going active with ATC will give you an improvement over passive but I'd still go with the passive 40s in your case.

Besides, the pro SCM20ASL is backordered at least a month, probably more; extremely high demand. You won't find it anywhere discounted below $6490 and good luck finding a used pair.