Mike Girardi has posted a review of the Synergistic Research UEF Tuning Circuits ($150) and XOT Crossover Transducers ($399) at Stereo Times. His conclusions:
“The employment of the UEF Tuning Circuits did not add its own flavor to the music but tended to enhance the energy balance between the fundamental and overtones resulting in the enhancement of low level detail. Employing the UEF technology in one’s system, allows the listener to easily discern the type of instrument and the subtle differences between instruments of the same type since the timbre is displayed so realistically. Further, the music is layered and textured with a lifelike three dimensional character. In summary, the UEF technology used in both the UEF Tuning Circuits and XOTs tackles the unknown and sometimes overlooked influence of high frequency noise present in all audio components. Highly recommended.”
You can read the full review here.