Did somebody say TOOBS?

The setup is actually very good having a solid state amp for the low frequencies, which needs a good damping factor, and a tube amp for the highs which can use the transparent midrange those amps provide.

The only thing I would watch out for is that if you are truly doing 'passive bi-amping' by keeping the speaker's internal crossover, the amplifier's gains must be the same or the high-low frequency balance will get altered. If the amps (or one of them) have input gain pots, this is not a problem. Also be aware of phase between the two amps. Listen around the crossover frequency area and change one of the amp's speaker connections for the smoothest response.