Ralph, your Atma-Sphere amps are known for, among other things, their superior reproduction of bass frequencies and instruments. In the technical details you provide for the amps, you cite their unusually wide bandwidth, possible only by not containing output transformers. One of the benefits of wide bandwidth, I understand, is less phase shift than is possible when employing bandwidth-limiting (i.e. all, to one degree or another) output transformers. Isn't the presence of those transformers in non-OTL tube power amps one cause of their often mediocre bass reproduction?
Transformer design and manufacture is a tricky business. One has to strike a balance between abilities at low frequencies (requiring a large transformer) vs. high frequencies (the smaller the better, all things being equal). Music Reference amps have unusually good bass because, amongst other factors, Roger Modjeski is an expert in their design, winding his own for some applications. Of course, no transformer is better than any transformer, but not without a penalty (amp-to-speaker impedance matching).