Harman Kardon HK990 Question

I pulled this amp out of storage the other day and hooked it up.  For the 1st time since I bought it, it occurred to me there is no way to bypass the high and low pass filter section when utilizing the subwoofer outputs. When the sub outputs are turned on, the setup process forces you to select a crossover frequency, even if you want to manage your bass via other options.  If any of you guys are still using this amp, how do you address this issue?  I guess I could just hook the subwoofers up to the preamp outputs.  My subs don't have high level inputs.