Between the Primaluna and ARC I would take the Primaluna even though I am not a fan a Chinese tube amps.
The RM-100 is a better suggestion.
Also, since the 1950s, ESLs and OTLs have been the 'match made in heaven'. This is because ESLs are a Power Paradigm device, see:
http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php
Now if you read the article you now know that if you mix the two technologies, Voltage vs Power, you get a tonal aberration. The ARC is more Voltage than Power (uses a lot of feedback); you will find it does not play bass on the Quads very well.
The RM-100 is a better suggestion.
Also, since the 1950s, ESLs and OTLs have been the 'match made in heaven'. This is because ESLs are a Power Paradigm device, see:
http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php
Now if you read the article you now know that if you mix the two technologies, Voltage vs Power, you get a tonal aberration. The ARC is more Voltage than Power (uses a lot of feedback); you will find it does not play bass on the Quads very well.