Searching for power amps with low damping factor.

Check out the NuForce - they have a damping factor of over 1000 or something.

Elberoth2...4000 is what they say.

I understand what you trying to do. As you mention some speakers do not perform well with amplifiers of high dampening. It can cause the speakers frequency range output to be unbalanced..which pretty much throws tonal balance out the window. Op chip amps have a low dampening factor. Not sure of the exact rating though. This is why many single driver guys use the Chip amps. They have control of the driver without taking the sparkle or the bass out of the music.

An enclosure that is designed to remove the need to control the backwave reflections/pressure of the driver. Allows the driver or drivers to work more efficiently without the need for a high dampening factor amplifier. The cabinet does the work for the amplifier and driver relieving them of the stress. IME the midrange seems much cleaner or open on speakers designed this way.

I've always thought high dampening factors equate to high negative feedback. Which IME isn't a good thing in large quantites. It will have your ears bleeding on the wrong pair of speakers that's for sure.

Good luck

Why not just put a resistor in series with the speaker. Not much power would be "wasted" for a big reduction of damping factor.

I forgot to mention the original Monarchy SM70 as a viable solution. Dampening factor should be pretty low. Pure class A, Single ended with no negative feedback.