HPF is an abbreviation for "High Pass Filter". Most pickups put out frequencies that are lower/more fundamental-heavy than we actually hear acoustically from just an acoustic bass. There is a physics-heavy explanation for this, but it's not needed; just think about how amplified bass often sounds too bottom heavy when things get loud and you'll know what I mean. A HPF rolls off the lows below whatever frequency you set it at, so you can dial out the mud and go easier on your speakers by letting them use their energy reproducing the frequencies you actually want to hear and rolling off the ones you don't. Fortunately for you, you live in the vicinity of someone who has an extra one lying around that you can try any time you want! Just shoot me a text if you want to borrow it.
I only have Phil Jones combos, so I couldn't say if the head alone would be the kind of sound that you are looking for. But you are welcome to stop by and try the combos and see if that sound works for your bass.