Don't worry about the dynamic head room spec - a lot of ss amps have a value less than 1.0, including the big ticket ones. This value can be relatively meaningless if the duration of the extra power is not specified.
As far as damping factor is concerned, a ratio of speaker impedance to total output impedance greater than 10 will adequately control most cone drivers. The speaker cable impedance has to be added to the amp output impedance for the total impedance. An amp with a low DF and long, capacitive speaker cables is the only reason to look at the DF if it's less than 50 or so, IMO.
Alone, neither one of these specs will tell you very much about how the amp will sound in your system and room.
As far as damping factor is concerned, a ratio of speaker impedance to total output impedance greater than 10 will adequately control most cone drivers. The speaker cable impedance has to be added to the amp output impedance for the total impedance. An amp with a low DF and long, capacitive speaker cables is the only reason to look at the DF if it's less than 50 or so, IMO.
Alone, neither one of these specs will tell you very much about how the amp will sound in your system and room.