Having used/heard almost all the ATC speakers with various amps, it is one of the most authentic sounding speakers in the world. Hence it is worth going the extra mile to give it what it needs.
SCM 11 is one of their easiest to drive speakers. You didn't mention your budget, but here are some obvious choices at various price points
Value for money
Naim Nait 5si - Don't go by their 50 watts rating, they rock hard and don't clip easily
Nice and easyATC SIA-150 integrated amp - straightforward match and good sound
TubeRogue Stereo 100 with a good neutral preamp - More expensive but more interesting sounding too
SCM 11 is one of their easiest to drive speakers. You didn't mention your budget, but here are some obvious choices at various price points
Value for money
Naim Nait 5si - Don't go by their 50 watts rating, they rock hard and don't clip easily
Nice and easyATC SIA-150 integrated amp - straightforward match and good sound
TubeRogue Stereo 100 with a good neutral preamp - More expensive but more interesting sounding too