Mapman, I'm not sure where you are holding with SS vs tube amps. But I think it's important to restate for emphasis sake that what Al and Ralph have been trying to explain all along is IME accurate.
If you read my posts about the SS/tube amp Paradigms and varying speaker impedances, I think Al was spot on when he said that an important factor, maybe the most important factor, is a tube amp's output impedance. The lower it is, the more "SS-like" it will perform.
I posted bench test reports from Stereophile and Soundstage for the ARC Ref 150 and ARC VS-115 (my amp). I found John Atkinson's comments quite interesting. He said that the FR output performance of the Ref 150 significantly "flattened" when driving a simulated speaker load off the 4 ohm taps as compared to the 8 ohm tap. Atkinson measured the Ref 150's output impedance to be lower off the 4 ohm taps as compared to the 8 ohm taps.
That result is consistent with what AL said about tube amps having low output impedance performing somewhat "SS-like" when driving speakers that were designed and voiced to be driven by a SS amp -- like mine.
Of course the reason the Ref 150 and VS-115 have low output impedance attributes is likely because of NF, which as Ralph says introduces odd ordered harmonics. So in the end, I guess it comes down to design trade-offs, with respect to both speakers and amps.
Bottom line: My Paradigm S8s have an impedance peak of 28 ohms at 2.2K Hz, which corresponds to the midrange/tweeter x-over point. In contrast, there is an impedance "saddle" of 4 ohms at 100 Hz. Paradigm advised me that the S8s were designed and voiced to be driven by a high current/high output SS amp. Ooopps.
I always thought the S8s sounded a bit "forward" when driving them off the VS-115's 8 ohm taps. At Al's and Ralph's suggestion, I tried the 4 ohm taps. I had to get used to the change in presentation, but now I like it better. Less listener fatigue, less forward, slightly crisper bass, and so forth. My anecdotal experience is consistent with what Atkinson predicted when he bench tested the Ref 150.
Not sure what else to say. Seems to me that if one can pick up a great speaker with relatively flat impedance and phase angle plots, the issue of tube versus SS amp compatibility will be largely mooted. But based on my read of reviews on some of the "big boy" speakers out there, like Magicos and Revel Salons, you are looking at speakers that need to be driven by some monster SS amps to sound their best. But don't take my word for it. Pull some of the bench test reviews and see for yourself.
Cheers and thanks again Ralph and Al for your patience and help.