ARC amp differences.

Save your money and buy Prima Luna if you must have tubes! ARC is over-rated and over-priced! If it breaks good luck with repairs before the next decade!

I have Sonus Faber Amati Tradition speakers and have powered them with the Reference 160s and Reference 160m monoblocks. I also auditioned the Serfino. They sound great, really a perfect match. I have also heard the Vsi 70 and the VT80. My listening room is quite a bit larger, which is why the Amati are the right choice for me.

The Reference 80s would be a great choice although I would not consider the Ref 160s overkill. The architecture of the two amps is identical, the 80 just having less power. They have exactly the same sonic character. I run my Ref 160 in the triode mode, so they actually only put out 70wpc. The difference is subtitle but very important. They are more musical in the triode mode. The reference 80s also has a triode mode, it puts out 33wpc in that mode.

I guess, if you can afford it I highly recommend the REF 160s. But you are unlikely to be disappointed with either. I listen at relatively low volumes as well. But they can be cranked without compression or distortion. 
 

Also, if you go this route I highly recommend Transparent wires except for the amp… I went AudioQuest Hurricane on that (big improvement). While I slowly migrated to my system (see under my virtual systems) to this combination over forty years without knowing this. The Audio Research / Sonus Faber / Transparent combination is a known incredibly synergistic combination, that really captures the gestalt of music as well as the details. I get lost in it about three hours a day and need to drag myself away.

Jasonbourne obviously has a beef with ARC. I've never had any issues whatsoever.  Primaluna is not in the same league as ARC. And yes I've owned both.