Which speakers will fill 5,000 cubic ft coherently

Davvie- But don't some Mac amps have internal autoformers? I could be wrong, but I think I read that somewhere.

Denis- I think you should get the Selah's. I've always wanted to hear them and they are beautiful ;~)

Unless I miss my guess, the output autoformers are essentially the same thing as using the speltz autoformers (which have different impedence multiplying taps), except that they are internal to the amp. So we are still back to the same issue; most tube amps (and esp. OTL amps) prefer/sound better with a high impedence load. However, (and here I may be wrong) the large # of output tubes in the bigger Atma and Joule amps, make them a better match for a lower (not low) impedence speaker (assuming a flat impedence curve) than might otherwise be expected.

Veddy interesting.... thanks for the clarification, Ralph. Of course, all other things are almost never equal ;~)