So, I'm feeling like a total impostor in this crowd, but I've done something not unlike this and much simpler in my system. I have a pair of SET amps monoblocked at 10 W each - the mids and highs are sweet but the bass is (was) pretty uncontrolled with my original speakers. Last year I went with two upgrades: a set of line transmission speakers with just a 4-inch driver, and a vintage McIntosh 250 SS amp. My preamp has two sets of outputs, one now leads to the McIntosh to drive a pair of B&W 500s and a subwoofer, while the other set feeds the monoblocks/line speakers. I essentially now have two separate systems driven by the same source, superimposed. I tuned the relative volume levels and balances of each system by ear. I wasn't expecting much but wow, I now have the sweet tube sound and a very tight lower end, it really worked. (The McIntosh side does a pretty competent job on its own, but the tube enhancement pushes this into another realm to my ears.) I'm sure this is still a junior system compared to what I'm reading about on this thread but I'm really enjoying it.

Cheers

Bruce