ATC SCM 40 vs. ATC SCM 50

If you go ATC then you really should consider their active speakers. The difference between passive and active crossover will make an audible difference in clarity and effortless sound.

Since you really liked the 40 then you will also like any of the larger ATC's as the voicing, design and timbre is almost all the same (probably unique in the speaker industry is the way that ATC sticks to a design for decades and that all ATC's, from the 20 on up, sound nearly identical). Larger models just increase slightly the clarity, dynamic range, max SPL and bass extension.

I prefer the passive. I won't miss the pleasure of trying different amps. :)

No problem - but consider that you can still play with your source and preamps (tubes etc). ATC built in power amps run class A to two-thirds power - three amps per speaker - something you will find hard to achieve in a powerful but separate class A power amp.

Shadorne, I hadn't thought about the amps in ATCs that much. If they run Class A... does the speaker enclosure throw off a lot of heat?

A fair amount (as much when they are idle as when you run them hard) but remember that the amplifier does not have to power a lossy passive crossover or handle large impedance swings - since it is band limited to only the frequencies necessary for the particular driver. This allows for much greater efficiency and optimization.

@digsmithd  

congrats on the 19's! Any pics?