The electronic crossover featured here is an 18dB / octave unit, and has the crossover frequency centred on 300Hz.
Be careful when adjusting the level of controls, since it is easy to create a mismatch in levels between the amplifiers. I suggest that the controls be mounted on the rear panel, with their shafts cut off really short, and a slot cut into the end with a hacksaw. Once the adjustment is made, it should not require further changes in use. Make sure that the power amplifier volume controls (if fitted) are turned fully up, and try to set the crossover controls so somewhere between midway and 75%. This ensures plenty of scope for getting the levels right, and will Ensure that the preamp settings are not radically different from their "pre-biamp" days.