Why fuss with tubes in an amp?
Not sure if serious........?
Why? Well because tube amps sound better than SS amps the vast majority of the time. I also have tubes in my phono stage and my DAC. They are just the preferred method of amplification in all applications if sound quality is a premium.
That said, I am not of the mind that all tube amps sound better than all SS amps. I have owned some very good solid state amps, but they usually don't hang around for very long.
Oz