BI-AMPING

In-line attenuators, as JMCGrogan suggests, will probably work fine. I happen to have volume pots on my ss amp that peform the same function, and that allows me to bi-amp a 170wpc ss amp with 60w tube monoblocks. Lovely sound, with the added benefit of being able to adjust the bass to taste. The result is smooth across the dynamic range.

I use a Sim amp for highs and lows and SET amp for mids with my Emerald Physics 2.3. I connect all speaker cables directly to drivers. The DCX can be used as room correction as well as gain adjustment for using multiple different amps. I would also recommend downloading Room EQ Wizard,which will give filters to input to DCX for room correction.

You can build a custom resistor network to eq both. Use Metal Film 0.1% tolerance voltage dividers. Put the divider on the bass only which is where you need it anyway.

Other option is to use a passive Pre such as Axiom. This is a cheap easy way out.

The side effect of both of them is the impedance matching and change. It won't be an issue on your bass however when calculating the voltage divider, you will have to consider the source and destination impedance. That is why the passive pre is easier/better. Insert this between the Amp and pre for your sim.