From the same review:
What is less good are the spikes overlaying the waveform at the signal’s zero-crossing points, which imply inadequate standing bias current in the Gaincard’s output stage. When RD writes about "a hardness or glare in the upper midrange and treble," I do wonder if that correlates with the presence of the high-order harmonics that will result from this behavior. Of course, RD also found that this character dissipated after a very long break-in period.
Lab 4706 Gaincard, 1kHz waveform at 22W into 4 ohms (top), distortion and noise waveform with fundamental notched out