No, you cannot actively bi-amp with the inboard X3700H AVR amps. To actively bi-amp a front channel speaker, you need to use an external electronic crossover connected between the channel preout and external amps. The AVR doesn't contain any electronic crossover.
I use the AVR-X3700H in my theater system. My 3 front speakers are bi-amped with QSC DCA 1222 digital cinema amps, using appropriate QSC electronic crossovers.
With regard to passive bi-amping, both amps cover the full frequency range and that is a waste of time. If the amplifier is not powerful enough, get a more powerful amp.