It's a passive tonestack which will be different to the usual Hartke EQs. If you turn the bass knob up, it increases the volume going into the mid and treble stages, and if you boost the mids it increases the volume going into the treble stage. If you turn all 3 knobs down, the amp goes silent. I'm not sure, but it sounds to me that if you boost the bass knob you may just experience a volume increase unless you reduce the mid and treble to compensate. And boosting the mids to get rid of the scoop should also boost your treble, so you'll have to reduce that to compensate.
This will confuse a lot of people used to more conventional modern EQs. But it's all meant to sound very nice anyway, so just tweak em until it sounds good!