Just plug them in with out an active crossover. You might need an attenuator on one or the other, but try it first without one and see how close they are -- you might not ned one, and its free to try! Pretty hard to hurt the panels with a 30wpc SE tube amp. Or the woofers with 40wpc tube. I doubt you could if you tried! Transformers give a lot of speaker protection. No DC to go to them.
Who made that passive attenuator that plugs into the amps RCA and has an RCA on the other side, for about $200 a pair? That would be ideal.
Tom