Perhaps even as important, if not more so, are the following other considerations: (1) the speaker's sensitivity; (2) the speaker's impedance curve as a function of frequency response; (3) the speaker's phase angle function, also as a function of frequency function; (4) was the speaker voiced to be driven by a SS or tube amp; (5) if using a tube amp, its output impedance; and finally; (5) room size.
A Class A amp may be a good fit if the answers to the above considerations are: (1) high, say over 90 db -- good. (2) if flat and steady at 8 ohms, especially in the bass frequencies. Very good. It implies possible good fit for tube or SS. Also, if a tube amp, the DF will be higher, suggesting better control of the woofer(s). (3) If flat and close to zero -- good. If highly negative (capacitive), especially in the bass region and coupled with low impedance, suggests the need for a current monster, or SS amp. (4) If a SS amp, most likely not an issue. If a tube amp, a high'ish output impedance suggests the possibility of acoustic coloration if the speaker's impedance curve fluctuates like a roller-coaster. Also, DF will be low'ish suggesting the possibility for loose and rolled-off bass control of the woofer(s). (5) Small room and sensitive speakers, good. Large room and insensitive speakers, could be a problem.
Hope that answers your question.
Bruce
