Regarding active bi-amping, I tried for several months, with a Pass XVR-1 (upgraded pot to Dact), and two pairs of Kell fpb 750mcx. Tried many alternative settings, with one pair driving directly the two 15" woofers of each speaker, and the other driving the remaining 3-way passive crossover. Measured, listened, changed, measured, listened, changed, many times.
The sound with just the passive external crossover, with the Duelund (caps/inductors) and Path Audio resistors is so much more open and fleshed out than biamping that I finally gave up and I am selling the crossover and second pair of monos.
I considered trying the new active crossover designed by Nelson Pass, the First Watt B4, that now uses top components such as discrete Vishay resistors and Toshiba JFET transistors (US$1500), but I decided I am done with biamping.
Quite happy about the sound of my system with my new external passive crossovers.