laid back stereo power amp

+1 re the Wyred 4 Sound ST-500 class D amp. When I got my first ever passive monitors for the desktop system (ATC SCM12 Pro’s) I needed an amp, and it had to run cool & fit on the crowded desktop. Took a chance on a nice, used ST-500, and from 1st hook-up that combo proved sonically ideal.

The ATCs have great authority in all frequencies for a 2-way and might sound a bit relentless with a bright amp. I'll never know, because this is definitely not a bright amp...like that ATCs, it has great authority from the upper bass on down. When I crank the, the sound is rather amazing. And when I listen at low volume, I actually get solid bass (few speakers will do that). 

I asked W4S if it was OK to stand the ST-500 on its side, and they said NP, it runs so cool it barely needs airflow. That’s what I did, and it works exactly as advertised...

I would look for an older Classe amp, there are plenty on this forum. The older Classe amp were made for Maggie's.  I use Classe CAM350's with my 20.1's...

6119, I see that you are getting the AVA amp.  I’m sure that will be an excellent choice.  Keep us posted on how you like the AVA combination.
Regarding laid back amp recommendations I second nypd26’s recommendation of B&K.  The older ones are very laid back and tubelike sounding and if you need a little more muscle but also laid back and tubelike, get the EX442 Sonata.  I’ve had several B&K amps over the years and they are indeed giant killers and great bang for the buck!

How about some older McIntosh amps - the MC 2125, for example.  Or the B&K reference 200.2?  Those are much less expensive options than some of the others suggested.

I really like my Rogue Sphinx with my .7s, so one of the Rogue amps paired with your tube pre might do it for you. Plenty of smooth power. I do use the 1 ohm resistors Magnepan provided for the tweeter section. I won’t recommend a Musical Fidelity MSi series amp if it’s laid-back you’re after. I tried the M2si And found it a bit bright for my taste. But if anybody’s after energy and zing, it’s got that nailed! I think MF makes good gear.