Here's what you can do in the System Architect software (v1.90):
LP "Bandpass Gain" control set to -10dB:

LP "Bandpass Gain" control set to +10dB:

If anyone is running Band Manager, please check if you get the same options? For some reason I couldn't get band manager to run on my computer.
It would be nice to just turn a control on the amp front panel to bring up the subs or tops. On the other hand, you can bring a simple laptop to the gig and adjust the settings. Connect a mic to your laptop and do RTA, adjust the Xti EQ section in System Architect. Try that with a regular power amp.