In amps with output transformers, damping factor is limited by the magnetic hysteresis (lag) of the output transformers, to usually not more than 16. This includes all tube amps with output transformers, and certain ss amps with 'auto-formers' (like McIntosh ss amps.)
The main advantage of higher damping capability is in providing cleaner bass in cone woofers and subwoofers. I think 100 is plenty, unless your speaker cables are 50 feet long! Speakers with big voice coils and strong magnets (woofers) create a strong 'reactive load' (a counter-current back to the amp.) Damping is a measure of an amp's ability to overcome this reactive load; to make the cone follow the music signal precisely and reversing its direction of travel instantly when the polarity of the signal changes.
This is why subwoofer makers use ss amps, as well as why people who biamp their speakers use a ss amp for the bass, and a tube amp for the mid/highs. (A tube amp has plenty of damping to control midrange drivers and tweeters, while, many believe, offering a more nuanced presentation of the music, especially the midrange.)
Speaker Q (actually woofer Q) becomes an important issue primarily when it has a resonant peak at a certain (audible) frequency; because the cone becomes hard to control when excited by musical information at that frequency. Adequate damping can help keep the woofer's response flat, but more important IMO, good damping results in better bass transient response (detail.)
Vintage Mac gear (tube) has the lower damping associated with tube amps, although Mac's tube amp damping is always a couple of points better because of their unrivaled output transformers. Their ss amps, (except for a couple of models - can't remember which) all use autoformers, and although they have a bit better damping than their tube amps, I wouldn't buy one, new or vintage ;-) As for what the folks at Krell said: well, if you're using a Krell, you don't need to think about damping ;-)
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