Are there any preamps that can work with 2 amps and a sub woofer?

Is your sub self-powered? If not, I would advise selling it and getting a self-powered sub with built-in equalizer.

Sub receives l and r from pre-amp, takes the low bass, sends only upper bass, mids, highs out to amp. Importantly it's volume is controlled by the preamp.

Adjust Sub's crossover point; adjust Sub's volume control to match your main's at your most frequent listening level. Now any volume change at preamp goes to sub and amp(s) cohesively.

3 sets outputs if you use the tape out, that would be a way for many others

https://www.ebay.com/itm/Audio-Research-Reference-6-Tube-Pre-Amp/324525777594?hash=item4b8f3e62ba:g:...

xaak

I wondered about tape out volume, it's been a while, thanks for clarifying that.