Srajan Ebaen has posted a review of the Backert Labs Rhythm 1.1 preamplifier ($7500) at 6moons. His conclusions:
“With the Mythology monitor and Jefferson Torno’s Grand Cru Audio Horizon as two very accurate informative high-resolution speakers, I preferred Backert’s contributions over Nagra’s. They hung more meat on the well-defined bones without going overboard like lesser transformer-coupled valve amps can. Regardless of speaker, a consistent observation was unusual bass power on extension and amplitude. For that we tend to think power amps because those literally drive the speakers. Extrapolating, should one think of the Rhythm 1.1 as a superior amp driver? It did sound that way.”
You can read the full review here.