Kal was right!

I'll be very curious to read how it goes, rpeluso!

I'm intrigued by these speakers and the fact you drove them with a tube amp is cool.  I use Conrad Johnson Premier 12s, 140W/side tube monos.  

I'm actually most intrigued by the smaller S5M monitors - the towers would be too imposing in my room and the specs for the monitors look impressive!

They are 92 dB/2.83V/1M. This is a job for a 100 watt plus class A amplifier. If you like tubes go for an Atmasphere MA1. This assumes subwoofers down the line. If you really wanted to knock yourself out of the ballpark Parasound JC1+s will definitely do it. 

Stereophile measured some demanding impedance though.

I wouldn't be too concerned in my case.  I've found my CJ Prem 12s to have little problem powering some demanding speakers I've owned, including my current Thiels and the brutally demanding MBL omnis.

Good choice….they were setup at Capital Audiofest last month. They were very impressive.

Without subwoofers, dont look to the Atma-spheres. Impedance is the issue not efficiency. I own MA-1s.