Amplifer with high damping factor will work well with any kind of speakers because the high damping factor will prevent the back EMF generated by the speaker cone during its motion of the moving coil in its air gap and will not affect the amplifier's output stage. More over in a TL the cone motion is reduced unlike a Vented enclosure due to absence of back-pressure from the enclosure wall. Also the speaker system impedance curve is reasonably flat in a TL and hence will have positive impact on the damping factor.
I dont quite understand the technical reasons behind this but would draw your attention to the following extract from this Nelson Pass paper: http://passdiy.com/pdf/cs-amps-speakers.pdf
Quote:
"The need for electrical damping is different for each type of loudspeaker and acoustic environment. High-efficiency full-range drivers are more easily damped than other types due to their powerful efficient motors and light cones. Looking at their bass response curves, we conclude that they are easily over-damped, resulting in excessive loss of bottom end. This partially explains the preference for tube amps with such loudspeakers. Anyway, this assortment of observations arrived at a confluence when I hooked up a Son of Zen amplifier (Audio Electronics 1997 #2) to a pair of Fostex 208Es in sealed enclosures. The Son of Zen operates without feedback and has an output impedance of about 16 ohms. This nets a damping factor of 0.5, miniscule compared to the 100 to 1000 you can achieve with regular solid-state amplifiers.
With the low damping factor, the Fostex became a totally different speaker. It suddenly had bottom end response and a better top end."
I own a couple of speakers with high efficiency full range drivers. My own experience has been that they dont like highly damped amplifiers.