Bryston vs Modwright?

Clayton Audio is a good recommendation, but I don't know if 50 wpc will be enough to drive those speakers.
I'd look into a Wells Audio Akasha, or a Innamorata if you can swing it.

I would go with the Modwright if only using your two choices. The Bryston would probably be too much yin with the ARC preamp and Dali's both being on the bright side of the fence. You need some yang to balance your sound.

Second the Plinius. Would also look at Audio Research Ref 75 with KT-150 tubes.

I have the Modwright KWA100SE driving Modwright LS100 preamp and formerly JM Reynaud Offrande Supremes and currently Daedalus Argos V2s. To my ears the KWA100SE is very pleasing sounding, not partial to one part of the spectrum, dynamic, non-fatiguing. I'll put the Argos aside as they are 98db efficient, the Offrandes are 92db and I never found having to crank the preamp above 10 in a 28x20x10 listening room. 

Meant to add, Dan Wright is very easy to speak to and willing to have a conversation. I'd give him a call and discuss your equipment, room, music tastes , etc. ; worth the call. 

One last point, my experience is that Modwright gear isn't partial to music genres. 

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