Question about external crossover with tube preamp

I'm setting up a new 2-channel system, and in my setup, I'm looking to use a tube preamp. I also want to use an external crossover of some kind, so that the sub handles the low frequencies, with the mains handling the higher frequencies. I'll probably cross at around 80 Hz.

My question is this: I know that when matching a tube preamp with a SS power amp (or a SS subwoofer amp), it's important to check that the Zout on the preamp is sufficiently low compared to the Zin on the amp. Im thinking it should be better to connect the preamp directly to the power amp, rather than connecting it to both a power amp and one (or two) sub amps, particularly since the Zin on sub amps can be rather low.

However, it seems like most people are crossing using an active crossover, which goes between the amp and preamp. This requires that the preamp signal go to both the power amp and the sub amp, which I'm trying to avoid for the reason above.

Is it generally a bad idea to use an active crossover with a tube preamp, or is it "okay" for some reason, given the impedance characteristics of typical equipment?