changing op amps, resistors, caps and wiring can significantly alter the sound, same with the connectors. suppose you want to create a certain flavor, the big companies would not change the parts in their designs.
i think there is another company that will design an tube amp for you , i think the name is nightshade. he makes a dac called the lampizator.
i think there is another company that will design an tube amp for you , i think the name is nightshade. he makes a dac called the lampizator.