Recommendations to upgrade my amp to pair with my Sonus Faber Sonetto IIIs

I would also consider a Rogue ST-100.  It is pairing very well with my Olympica iii.  Audio Research as mentioned above is another great choice. 

Audio Research is part of the well known synergistic combo of Sonus Faber, Audio Reseach, and Transparent cables and interconnects. I independently discovered this combo over a period of fifty years. Once, I had all SF and ARC gear with Transparent I started seeing references to it. You can see my system under my ID. For you, I would look for a used Ref75. Save up if required… what you have should sound good.