I've used the gfp with Sonic Frontiers, AR and mccormack amps. I didn't think it mated well with the AR amplifier. There was quite a difference in sound quality using the preamp verses the CD direct. I recently put one together with the mccormack and find that the system actually sounds better with the preamp (in passive). The active mode isn't bad either, but does lose a little detail. I find that my tuner doesn't have enough oomph (how do you spell oomph?) to drive the passive mode well.
