The number of tubes increased as speaker efficiency decreased. Paralleling tubes or going push pull can increase power but also can muddy the sound. As a builder of SET amps I focus on using as few tubes as possible. Each tube has its own sound due to its harmonic signature. To many harmonic signatures can lead to a softer or muddy sound. A well set up SET can be as detailed solid state amp. With the addition of a level of harmonics that keep it from becoming sterile. But you are back to using efficient tubes.
As to using a giant 50 or more watt transmitting tube. They are hard to power their heaters.
As to using a giant 50 or more watt transmitting tube. They are hard to power their heaters.