@o_holter I love tube amps also, I don't know of speakers that are made for tube amps, the dampening factor for a solid state and a tube amp would be very different, generally tube amps don't have near the power of SS amps of course, it there were speakers that were designed for a tube amp that would be a big deal and I would go out and buy it.
@kota1 is right outboard crossovers, at line level, then amplified to a speaker that was designed for that particular tube amp would be amazing. @kota1 probably knows of a company that does just this, that's the answer.