ATC has many models, Active and Passive, some designed for Pro Audio and some for residential use. The cabinets and finishes are different. The Pro line has black paint and completely different driver layout until you get to the 50s. The sound quality is pretty consistent across the line. It just gets bigger and better as you go up.
I have ATC SCM50 Passives and like it that way. But I have options. I can swap out the back panel and install an amplifier pack, converting them into active. I believe that currently costs about $8k. You could certainly spend a lot more on an amplifier but would it be superior to ATCs matched, hand built amps designed specifically for that speaker?
So for me, if I wanted to upgrade my amp, I would probably opt to just go active. In that sense, it’s a bargain. But my longer term plan is to biamp them with a tube amp covering the mids and tweets.

