You got low damping factor pretty much spot on.
Not modern (and no measurements available that I'm aware of), but I have a 20 year old Musical Fidelity X-A1 SS integrated amp that seems to have a very low damping factor as I've used it with many different types of speakers and it mimics the characteristics of a tube amp with "measured" very low damping.
I've had to open it, and the separate power supply, a few times to remedy what was basically shoddy assembly work and discovered that it had wire wound resisters on the speaker outputs (one per channel).
I also have an early 80's Carver SS receiver that also sounds as if the damping factor is quite low (Carver MXR130).
Anyway, hopefully switching to DC on your artisan amp will remedy the hum you are getting.
Also, definitely try the sub you own as doing so should give your single driver speakers a helping hand (making them richer/fuller sounding - more effortless) if the sub settings can attenuate the low frequency output of your single driver speakers.
DeKay