I own all three models.
There are a number of great amps that can power these. They work well with 60 to 100 watts pc minimum, solid state over tube.
Great candidate amps include Bryston, YBA, Exposure, Chord, Roksan, NAD and LDF. Expect to pay between $1,000 to 5,000.
Better yet, just buy their active line and be done with it.
Each of the above amps will impart a slightly more forward or relaxed sound within the speakers. I personally like the Exposure 2010S with the 7s, NAD's M series with the 19s, and the YBA Passion with the 11s. There are particularly good historical write-ups on www.sonicflare.com and Positive Feedback about ATC products.
There are a limited number of audio specialists around ATC gear. I can recommend Sound Asylum in Venice, CA. James Gregan is an excellent source for matching specific electronics--has handled the line for a decade and always has inventory on hand.
A fellow audiogoner named Shadorne regularly speaks of his ATC speakers. You might want to ping him as well.
I have been using these for almost 20 years. I have a live touring company and also own the 150s. I personally love the build quality of these (bomb proof)and how they play all genres of music well. You hear exactly what the recording is--very little color added--as thin and neutral as can be. The sound is not for everyone and they love to be played loud.
With that said, I am the biggest fan of this product line. The quality is present through out the line, and surprisingly, not much sonic differences between models. The 19s will sould better "out of the box" and you will need to burn in the 7s and 11s about 500 to 800 hours at least.