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?
If you want to cut off your main speakers at 80 Hz you will have to have either an active crossover or a passive attenuater between the amp and pre. The option is to run the main speakers full range and run a parallel set of signal leads to an active or passive crossover driving the sub amps. I use REL subs, which give many options and I recommend. There are other powered subs which do similar things. I think any of them would work well with a typical tube preamp. With an external crossover it would depend on WHICH crossover and WHICH preamp but most should work well, consult the makers of the units under consideration for best advice.
I should have added that I also wanted to avoid running the main signal through an electronic crossover, as I have always heard a degradation in the sound quality when I did so. Others disagree. With the RELs I set the subs to start rolling off at 25 Hz at the top end. I think 60 is too high, let alone 80 , for a sub used for music reproduction. HT has different parameters.
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Interesting Bob, I wasn't aware of that. Is this also true for a non-powered unit, like the Marchand XM46?
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I use exactly the type of set-up you're describing. A tubed ARC preamp (LS 25) feeds an NHT X-2 active x-over. The NHT high pass out (signals over 75hz) feeds an ARC VT 130SE. The main speakers are usually Ohms, but I also ocassionally rotate in Maggie or Verity speakers.

The low pass out of the X-2 feeds a Velodyne SMS-1 subcontroller which allows for digital room correction and fine tuning of the high cut filter characteristics for the sub's top end roll-off. This signal, in turn, feeds 2 Rythmik 12" subwoofers.

The results have been enormously satisfying in a very tough room and the NHT X-2 has little to no (to my ear, anyway) impact on the main signal path.

As always, YMMV.

Good Luck