Sorry Unsound, it's been way too many years since I've had a Threshold amp on the bench, or looked at a schematic of one, to comment intelligently. I seem to remember the Stasis output stage resembling the complimentary-feedback-pair configuration . . . which is pretty similar in behavior to a conventional emitter-follower arrangement . . . but I could be completely wrong.
Magfan, if we're going to actually go down the road on amplifier stability . . . then the main thing is for the designer to accurately analyze the phase margin across the ENTIRE bandwidth of the amplifier - and this can be a challange with one (i.e. the vast majority) that uses a tranresistance amp for voltage gain, as this is the one configuration of a bipolar transistor where the gain is highly beta-dependent. Usually the open-loop gain follows a first-order slope over most of the audio spectrum, making the phase margin 90 degrees into a resistive load. So it's usually a capacitive load that causes the alarming decrease in phase margin, hence the use of an output inductor (and frequently a parallel Zobel network) within the amplifier.
Magfan, if we're going to actually go down the road on amplifier stability . . . then the main thing is for the designer to accurately analyze the phase margin across the ENTIRE bandwidth of the amplifier - and this can be a challange with one (i.e. the vast majority) that uses a tranresistance amp for voltage gain, as this is the one configuration of a bipolar transistor where the gain is highly beta-dependent. Usually the open-loop gain follows a first-order slope over most of the audio spectrum, making the phase margin 90 degrees into a resistive load. So it's usually a capacitive load that causes the alarming decrease in phase margin, hence the use of an output inductor (and frequently a parallel Zobel network) within the amplifier.