Well, Chicago Symphony Hall has had its critics about its sound quality since it was renovated in 1997 - see the Wikipedia article, so who knows what he regards as "ideal" live sound. And of course, the sound of a concert hall in recording, which, except for the occasional live recording, is done with nobody in the audience, sounds different from the sound at a live concert packed with people. Live sound is actually notoriously variable. The sound in the front rows can be drastically different from the sound in the upper balcony - I remember sitting in Boston Symphony hall in the upper balcony decades ago at a concert which sounded like a muffling blanket had been placed over the whole orchestra.
So, no output transformers. Input transformers maybe to boost the gain? Or current source loads on the 6SN7s to boost their gain to the max? And incidentally, I found a Bell 300B spec sheet that shows current/voltage curves to 700 volts, so it can put out about much voltage as a 6SN7GTA if properly driven - more current, though.