Electronic cross-over on pre-amp out, to split signal to subwoofer and bookshelf speakers

I split my preamp output between an active low pass crossover to an integrated amp that feeds the main woofers and subwoofer (<63hz) , then to an inline high pass (10nF silver mica cap) to the main tube amps that feed the midbass/tweeter.  It has worked extremely well and has made the tube amps and midbass/tweeter modules sound notably clearer.  

The active crossover is just a cheap Pyle automotive unit fed by a wall wart.  It's fine below 80hz, but I didn't want it feeding my tube amps, which is why I opted for the inline filter using the silver mica caps for the high pass.  

https://photos.app.goo.gl/EdbW2F9jchcFrDFu8

Relieving the tube amps and the midbass drivers of the bottom octave or so should reduce distortion on both.  Those large frequencies hog a lot of power from the amps and cause large excursions to the midbass drivers.  If you can find out your amps input impedance, you could try a couple of inline filters (I used 10nF silver mica caps at a cost of < $20)

80hz-ish is a good option for two reasons...it keeps the sub playing in the range where it isn't directional, and it leaves just about the entire vocal range to the midbass driver. 

If you don't already have a sub, you might consider using two subs to help break up room nodes.   Most subs already have a built in low and high pass crossover, which could make it really simple to try.