I tried my O/93's with a very good SET no feedback amp, an Ampsandsound Nautilus with 8 watts and the sound is sweet but the firmness of the low end and the extension of the treble disappeared.
I can understand that outcome depending on the particular SET amplifier. Looking at Dave's pictures it's clear that his amplifier has very robust power supply and he mentioned custom quality output transformers. So for him, no problems controlling the bass .
Charles