Subwoofer for classical music listener

I owned REL Storm III and loved it. I tried line level and speaker level connections. I really liked what the sub could do for my system. Bought a measuring mic and learnt how to use REW. So I could measure the impact of varying  placement.

Later I bought 2 Rythmiks 12" kits and built sealed, very heavy (100 lb each), rigid boxes. For less than the REL I got better sound. Rythmiks are servo driven and also have a lot more controls for fine tuning. It was a lot better than the REL.

Eventually I went from the pre (Lamm LL2) to the subs xo and from there to the tube power amp, relieving the amp and speakers from attempting to reproduce below 80Hz. Yet another improvement. Like the article linked to earlier said. 

If you extrapolate the reasoning in that article you arrive at an active system. Later I did without the preamp altogether  abd went active. Running digital xo at the software level, adding time alignment of the sub and midbass woofer, and adding room correction is yet another leap forward. Despite this being a paradigm shift for most audiophiles thinking digital xo are detrimental. I know I'm not going back.

@Steakster, I don't think it's possible to answer your question without a lot of additional information, including the things you mentioned that cannot be determined, and also:

-- The input impedance of your power amp.
-- The length of the cables that connect the preamp and power amp.
-- Whether the outputs of the tube preamp are capacitively coupled or transformer coupled. (Or if it is one of the very few that are direct coupled, e.g., those made by Atma-Sphere).

Generally speaking, though, I would consider using a tube preamp to drive both a power amp and a pair of subs, at least one of which has an input impedance as low as 12K, to be cause for concern. Especially if the tube preamp has capacitively coupled outputs (as most tube preamps do), since the resulting output impedance most likely rises considerably in the bottom octave or two from what it is at higher frequencies. (The impedance of a capacitor increases as frequency decreases).

Something you might consider, though, would be trying to find some sort of buffer stage, that would provide a high input impedance and a low output impedance, and inserting it in the path between the preamp and the subs. Or, if the main power amp also has a low input impedance, perhaps inserting it in the path between the preamp and both destinations. Something like the Burson Audio buffer stage that was marketed some years ago, but is no longer made.

Best regards,

-- Al