Biamp question

Yes just split a full signal out to your preamp to you SS and Valve power amps. RCA or XLR. What ever you use.

Enjoy..

You’re fine OP. You don’t need anything BUT two amps and cables. You have a good idea. SS for the bass and Valves for mids and highs. The Parasound will have the greater gain. It is a plug and play thing. It will take more time to route the cables than anything else. Remove the jumpers between lows and highs on the speakers and plug in. Adjust the Parasound. DONE.

Side Note:

You need two of the same for vertical bi-amp. You're using them horizontal. I've biamped for 40 years horizontal, NEVER vertical.
I quit using Valves for bass 40 years ago too. Just a bad idea in reproduction, not to mention the heat.
Only one time I didn't bi-amp and I fixed that soon enough. BIG fan of bi-amping with SS and tubes. 

I forgot, Merry Christmas and Enjoy...

Regards

I'd be careful with and active crossover that doesn't fail safe. A Behringer DCX2496 will fail to work but not send the wrong signal to the wrong place. I only use an active XO in my Bass management system. I find there is a lot better protection with a passive XO for mids and high. 300 hz and below I'm direct coupled too. No passive crossover. I don't recommend it, out of the gate though.. Hook up your amps and be happy. Quit making it complicated.. You want to mess around later, you always can.

Regards