But what I read was, "is it possible or advisable to use an RC network between the preamplifier and HF amp when going active?"

I just had it in my head that's what you meant when I wrote my reply.

Anyway, you can put reactive components in between the driver and power amp, just like if the system were not bi-amplified. But that limits your benefit from using a bi-amp implementation in the first place. In some cases, adding reactive components in the high current (speaker output) side of the system may be the only option. But in all but a few cases, I would recommend that you remove the crossover components from the speaker circuit and install them in between the preamp and main amp instead.