Which technology is a better match for my Parasound Halo A21?

The Parasound Halo A series is going to do well no matter what you throw at it in terms of modern speakers. They are pretty well constructed, low impedance amps.

I would focus more on your room acoustics and placement.

The only other consideration is they are very neutral to warm amps. If you need extra detail, they won't give it to you.

On the other hand, with ESL's they have plenty of current at the high frequencies to prevent them from sounding dull, like lesser amps might sound.

Thanks, erik. I read a lot about the different loads, and it seemed to me like the Halo could handle most anything, but always nice to hear some confirmation. My speakers are (and would be) placed about 30" from the back wall and several feet from the side walls. The room is wider than deep, treated with heavy tapestries front and back walls, and sound dampeners in the high corners. The speakers are now about 7-8’ apart (with room to spread), and about 10’ in front of the primary listening position, toed in to cross just in front of the ear of the listener. This seems to be the best for the Motion 20’s, but the sweet spot is a little constrained for my liking. The highs and mids are clean and sweet, and the lows tight and controlled, but as everyone wonders, can it be better???

This may be a bit off topic, but does anyone have any experience with the BG Radia 420i’s? I see a pair listed and they kinda caught my eye.

Hi I used the Parasound Hint which has less power with Maggie 1.7i and the combination was pure magic. Never had to turn the amp past 10’ , the combo had plenty of everything. The only time I heard ML was at a Best Buy and wasn’t impressed but it could have been their set up.

Thanks, johnto, I would bet that Best Buy's setup wasn't driven by anything close to the Parasounds.  I know the ML's have a narrow sweet spot, and positioning is everything, so,,,,,,,,,,,,