ATC active vs. passive

I’ve no experience driving ATC speakers with tube amplification.  However, I abandoned tube preamplifiers as they were simply too slow for the speed of the 40As and 50As.  This happened with my Manley Jumbo Shrimp, Manley 300B and highly modified de Havilland.  I moved to Sugden and Luxman C900u.

Also run passive ATC 20s with SS and 7s.

The 150 is a physical monster.  I hired piano movers for a second story location of my 50s.  Best of luck with the quest.

I have a pair of ATC SCM50 passives running through a c900 and m10x pre/power combo.  For me this setup is all I will ever need.  Silky smooth at low volume and that's retained at much higher DB.  They match very well.  

Another variable to consider is in the active option, is it using DSP or using analog xovers?  You can have active but without DSP.

If using DSP, I am assuming the speakers take the digital signal directly from the cd player, perform DSP, then using an internal DAC to convert it back to analog before feeding it to the internal amp.  

For example, if you have a 3way speakers, you will need 6 DAC, three for each channel, which won't be cheap.

I bought ATC scm40 and powering them with luxman 595, MASTERSOUND 845 and Grandinote Shainai integrated amp. 
I like the tonality and happy with low end. However, the tweeter is inferior to my Triangle Magellans. I’m still interested in ATC 50 and 150, hoping the tweeter is a big upgrade from the 40. 
if I get the 150, I probably won’t have enough to upgrade my amp for a while. Hopefully luxman 595 is enough. 

OP,

Your thoughts on the larger ATCs are justified. I can still recollect the boogie factor on the large ATCs. They were playing Daft Punk’s Loose Yourself to Dance. It was late evening and I was tired. But still felt like dancing! Stayed back in the room till the song finished. Go for it, if you can. You can get a powerful amp later. I believe they were using some Audionet amplifiers, if I am not mistaken. But a memorable experience.