I think that I've had at least one of every version of the Rowland preamps over the years. The Concerto is a very nice piece at a very nice price point. In my experience the lineup stacks up as follows (from good to best).
Synergy
Synergy II
Concerto
Coherence II
Synergy IIi
Coherence II Series II
I'm ignoring the Coherence One, Consummate, and Consonance in this listing since I haven't had recent experience with any of them.
Performance between the Concerto and Synergy IIi is close, but the Synergy has a better (and more isolated) power supply along with better component separation within the chassis. The circuit topology is nearly identical with the primary difference being the removal of the additional circuitry to manage settings on a per-input basis and record outputs on the Concerto.
According to Rowland the performance between the Synergy IIi and Coherence II sII is nearly identical, but in my evaluations the Coherence II sII has always bettered the Synergy IIi.
Keep in mind that all of these pieces use a nearly identical circuit topology with the main difference being the power supply and quality of components. They all have a very similar "sound." The newer pieces (Synergy IIi, Concerto, Coherence II Series II) all use surface-mount technology in the construction of the circuit boards. This results in a much shorter signal path and a lower noise floor.
Again, there's nothing at all wrong with the Concerto and it's definitely a very nice sounding piece.
