If all amplifiers sound the same and a cheap amp is as good as an expensive amp - where is the market for a complicated, complex and necessarily expensive Harbeth amplifier ?
In the past ten years, I can think of possibly, two customers who have enquired about tone controls - so it's not a big issue. As for DSP, I think it's a complete non starter. I've never yet found a room which couldn't be improved sonically by the judicious use of a few curtains and carpets. Why pay for complicated electronics ?
The Harbeth customer is looking for high quality, good value and invariably, two channel music, with no frills and gizmos.