I have the GCC-250 (Stereo control amplifier @ 250 Watts). I find it quite nice, full sound, plenty of power, tight control top to bottom of the frequency range. Didn't to much A/B testing of amps so can't give you many comparisons. Before the GCC I was using separate PS Audio amp and pre-amp. Before that I was using Antique SoundLab (tube-based) amp.
I love the sound from my current system, with a Lite DAC-60 (via GR-research) tube-based warming the sound just a touch, feeding into the GCC. Absolutely realistic sound!