Which speakers will fill 5,000 cubic ft coherently

Fair comment, Macrojack.

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 ;~)

03-19-08: Springbok10
I'm not arguing about any of your points, tvad, just reporting what Ralph said based on Ty's conversation and Ralph's knowledge of the speakers.

Nor am I arguing any of your points. I just wanted to know where the Tyler minimum impedance info came from. Thanks for the answer.

Good luck on the hunt. I'm sure you'll find something great.

Swampwalker-

Yes...The MC 352 does use output autoformers.

To quote McIntosh...
"Output autoformers, a feature of many of our amplifiers, assures that you get all the power you paid for. Other amplifiers, optimized for 8-ohm speakers, have warnings not to use with many speakers that are 4 or even 2-ohm impedance. Others are optimized to work with these low impedance speakers, but deliver only a fraction of their potential power with 8-ohm speakers. Output autoformers avoid this problem, with separate connections for all three popular speaker types, insuring full power, without stress, into any speaker regardless of impedance."

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.