ATC SCM's with Spectral Components

I'd tend to go for the SCM19. ATC's all sound similar - but there is more transparency, SPL and bass extension as you go up the line. The 19 has the same mid bass driver as the pro models but with a simpler modern cabinet construction and different tweeter (so it is great value and has been road-tested through years of home and studio use - think Toyota Land Cruiser). It is a bit early to tell if the 11 will be equal to the legacy of the driver in the 19.

I can't say how it will sound - no experience with Spectral. All I can say is that 90 watts is just enough to drive them and ideally most people want 200+ watts. They are not hard to drive but the sensitivity is low and the pro driver can take darn near everything you can throw at them without flinching - so they sound good when driven hard and loud.

Things I've read seem to suggest they require more than modest power (i.e., 100 W RMS might not be enough power), and that they sound best when played loud (in not-so-small rooms).

They are leaner in the bass then most other designs (flat with no bass hump and a gentle roll-off). You will need some bass boost (tone control) if you listen at low levels. When you get up to live music levels then they sound most balanced (other speakers may tend to sound boomy or bloated at higher levels). Horses for courses - if you listen at low levels then ATC might not be ideal for you.