We tend to publish limited specifications, and do not publish damping factor (DF) specifications of any kind as they are highly dependent upon test conditions (speaker and cable impedance, as well as frequency and duration of the test) and as a result, like so many specifications, are not a reliable performance predictor and can even be misleading (as higher is not always better).
That said, high DF (or low output impedance) is important for the amp to fully control a dynamic driver's "pistonic" movement (forward and back). The amp will push a cone forward by applying current through the voice coil surrounded within the magnetic field formed by the magnet. Then the speaker cone comes back, moving the coil back within that same magnetic field and as a result creates a current that goes back to the amplifier. An amplifier with lower output impedance, aka higher damping factor, will absorb this incoming current better, with the general assumption that the amplifier will have more control over the driver.
However, this isn't linear, as a higher DF does not necessarily mean higher performance. There isn't much benefit between a DF of 1000 compared to a DF of 80. Most of that excess DF is lost in the speaker cables, crossover and voice coil (amplifier output impedance plus the impedance of all that wire and electronics). Anything above 80 is good. Only once you are at 25 or lower might there be audible artifacts.
Some manufacturers have been claiming DF figures of well over 1000, and as much as 2000 and 4000, leading consumers to believe that these amplifiers must provide superior performance as a result of having a higher DF rating than others.
What is interesting to note, is that many highly respected tube/valve amps have very high output impedances, with their DF in the order of 8 or 12, usually always under 20, but are often thought to be some of the best sounding amplifiers available, and in many cases as a result of their natural sounding bass.
There is even a very well-regarded solid-state amplifier manufacturer that keeps their DF at around 20-24 to maintain a house sound that consistently receives rave reviews from publications and the public alike.
With this in mind, there is some thought that an extraordinarily high damping factor may lead to an amplifier being overly damped or controlled, leading to a cold and lifeless sound, particularly at low volumes where bass may sound diminished.
But, in the final analysis, none of these specifications can indicate the sound of an amplifier, so we tend to disregard most specifications as indicators of performance, knowing that the only true test is listening. In fact, we find that most significant audio improvements we make to our designs have no impact on the measured response or specifications.
But, so as not to disappoint, Primare amplifiers have very low output impedance, resulting in damping factors of 100-450 depending upon model and system conditions.