That's a super high quality cabinet with massive low end. You should be able to easily hear the difference with and without your 80hz HPF. The Quilter heads definitely do not have a built-in, always-on 80hz HPF. That would be an absurd "feature" in a bass head.
@Rocknroller4 brings up a good point: Which patch are you using for the HPF on the Zoom, and are you 100% sure you are actually using it as a true HPF?
What about if you power off the Quilter and use headphones plugged directly into the Zoom? Can you hear the difference the HPF makes in that scenario, through the headphones?