Best amp for Sonus Faber

Until you share what specific improvements and sound characteristics you’re looking for this is just a crapshoot.

I've used big Chord SS and it was spectacular and now an Audiomat Solfege Reference 20 with my SF Guarneri standmounts. Not a big sample size but do know I didn't like YBA and Naim electronics. The Chord and Audiomat really manhandle the drivers and provide the impact I prefer. Just my experience

It is easy to conclude that tubes are a lot of work. Before I retired, I never changed a tube, even though I had some components for six or seven years. Now that I am retired I listen to music a lot more. So, I just changed the tubes in my preamp and amp after four years. I have had no "interesting" experiences with tubes other than incredibly great, musical and natural sound quality. If you listen to a hour a day depending on the application it is likely they will last ten years, often small tubes, more. 

I have Accuphase T-101,C-200 & P300 driving KLH Nines. No one has not liked immensely the sound of the system. I do recommend any original, not counterfeit Accuphase products made in China. I was going to bring my T-101 to get repaired at JustAudio in Baltimore MD because the center tune meter didn't respond, wasn't able to get any stereo stations or have the stereo relay illuminate the front panel light. Tuning was extremely noisy as well. Totally unusable. Visually inspected circuit boards, checked a few caps and resistors to verify functionality and finally I cleaned the oxidation from 6 x 6 PIN header and receptacles on both boards and the tuner has been restored to it glory, listening to WQXR in NYC, the stereo separation and super quiet background is a JOY to listen too after having it lie dormant for 7 yrs. Saved a 6.5 hr trip to Baltimore and back. Very happy

By the way IMHO my KLH Model Nines are pretty flat across the board and no matter if I'm using my 90/wpc Futterman H3A or Accuphase P300 or McIntosh MC250, they all sound good. What matters as much as the room and quality of source material, is knowing the listeners specific hearing response curve by an audiologist and compensation for any loss especially in upper octave with a high quality 31band EQ. REW and associated Umik1/2 calibrated mike's make a fun tool in understanding how everything works together.