I'm driving my 5As with 60-into-8 Atma-Sphere M-60Mk.3.1s, and FINALLY I've found an amp(s) I probably will keep forever. There's no lack of power--the system plays louder than I'd ever want to listen in my largish 3200CF room, and it never sounds dynamically compressed. Of course, one reason for this is the reduction of bass energy the amp(s) has to reproduce, since you'll be using some version of V-steen's hi-pass filter required by the 5As (and Quatros and 7s). Also, damping factor is simply not a factor with the 5As, since most of the bass is reproduced by that magnificent-sounding powered-bass system.
Go for the Mac, Tubes.
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