Recommendation for ATC SCM150 Amp/Pre

I may be out of line here, especially never having owned ATC speakers, but isn’t one of the main draws and benefits of owning ATC speakers having the on-board amplification?  Dedicated amplifiers that are matched to each driver seems to be an advantage.  Hopefully, you have researched this thoroughly with the dealer/manufacturer and with other ATC owners so that you are confident you are not missing an opportunity.  
Considering your stated tastes, does ATC offer the option of on-board power for LF drivers only? That way you could consider an active cross-over and run tube amps to power only the MF/HF drivers. Just some thoughts.

Congrats on your awesome new speakers!  I sold ATC speakers for a bit, and if it was me I’d get a Class A amp from the likes of Boulder, Pass, etc. and pair it with a tube pre that would be the Spatial Audio Raven, but the Aric Audio Motherload XL and Backert Rhumba Extreme or Rhythm would also be well worth a look, and all three offer trial/return period.  This is absolutely the way I’d go given what you’re looking for.  The Class A amp will give you some warmth and fullness in the mids while providing all the current the ATCs definitely need, and the tube pre will likewise provide great tonal properties/soundstage and inject some life/tube magic into what is ostensibly a studio monitor.  I would not recommend tube amps with your speakers at all — it’s a mismatch and you won’t get all your wonderful speakers are capable of.  Restrict the tubes to the preamp and you’ll be more than fine.  Just my $0.02 FWIW, and best of luck.  

I would definitely reach out to Aric at Aric Audio to discuss having him build a Motherlode specific to your needs. I have had mine paired to the Coda Model 16 to drive some pretty  inefficient TAD speakers and the sound is sublime. 

@ei001h congrats on those ATCs! I have the SCM40 v2 and drive them with a Simaudio Moon 761. Stunning synergy. Up there with classic synergy like Luxman/Harbeth. The 761 shares the same MDCA tech as the 861 amp, which is what you should audition if possible. The 761 to my ears, is lighting quick, effortless in delivery, and just wide open across the board. Natural harmonic portrayal is a major strength (colors abound)! Sound is overall very authentic and natural. The 761 really brings out a special midrange from those amazing ATC drivers. For the massive SCM150’s I don’t think you can do any better for the 20K price point than an 861.
For preamps you might want to consider Backert Labs Rhumba Extreme 1.4, or Rhythm. I have the Moon 791 which is astonishing for an all in one streamer/dac/preamp but it’s probably likely you can get even higher performance from all separates. As they say, the sky is the limit as long as money doesn’t run out. Definitely check out the new moon amps!

@soix 

Thanks for the recommendations. I currently have scm40 and could certainly see the difference with a high power SS amp compared to tune. I auditioned Electrocompinet 300w monos and I was blown away by what these little speakers could do. This is why I went for 150s.