After a couple days listening to the SST Son of Ampzilla II and comparing back and forth with the Bel Canto it is clear to me that the SON has a nice open top end; it has very detailed high frequencies but lower frequencies seem to be subdued. I would say that both the T+A and Bel Canto have very pleasing and articulate high frequencies, very inviting sounding and I would also say that both are more full range and musical. These two are more similar and the SON is definitely a different sounding amplifier all together.
The biggest difference in the three amplifiers is how they handle the lower frequencies. The Bel Canto and T+A amplifiers both have very tight and present bass while with the SON the bottom end is a bit loose and not as present. It feels like the room is too reflective and emphasizing the high frequencies while the other two amps are more balanced, like the room has a nice mixture of reflective and absorbent materials. With the SST amplifier I felt I might need to use a equalizer to balance it out a bit more, and I never use an EQ.
Now granted these differences are subtle, but definitely there. I would say the T+A is the most musical of the three, however with my Magnepan speakers having a bit more power is desirable, not that I listen loud often. Therefore any of the three can get the volume to a nice level for me, but the T+A has to be pushed a bit more. Therefore the SST and Bel Canto amps definitely provide a bit more of the power that the Maggie's crave. These two amplifiers definitely give a completely different flavor of power and both provide a bit more dynamics because of the reserve watts.
Any two of the three would make a nice complementary change of pace of the others. The Bel Canto I would consider my "main" amplifier at this point. I am not sure which I would rather have as the secondary "change of pace" A/B amplifier versus the Class D Bel Canto. The more robust power of the SST or the more articulate musicality of the T+A. We will see how it all plays out as I continue this comparison endeavor.
As an added thought; I do also have my classic McIntosh amplifier to throw in the mix. While not as dynamic or detailed as any of these "modern" designs it provides the classic McIntosh sound. So for a true change of pace and especially for certain types of music it is a pleasure to occasionally pop the speaker wires on to the MC754. For acoustics and vocals it is silky smooth and provides a listening experience that is to die for!