So I did my comparison today, the bryston 3bst and 7bst in parallel and serial on my Thiel 3.7. As both amps are off the same generation, they sound sonically identically. I used some jazz music, with organ and sax (domnerus, antiphone blues) and Brubeck, take five. First observation: the spl of the 3bst and 7bst in parallel were the same so comparing both in mono was very easy. Second observation: at 80 dB, what I consider at live loudness, both Amps were easily able to reproduce the music as I was seated 12 feet away. The only difference I could consistently detect was in the low bass where the 7bst was fuller. Any differences in the upper range, was undetectable by me, no signs of any distortion. 3. But then I played some female vocals, brendi carlille, and there it was, her voice was deeper on the 7bst and sharper on the 3bst. Enough of a difference to keep the 7bst.