@fdeck would know how his HPF3 would get you there. Maybe he'll stop by.
Thanks! Much as I love the HPF, I always suggest giving it a try without one. There's no reason to carry extra gear if you don't need it. I get an employee discount, so of course I use one.
Many amps designed for electric bass are "voiced," meaning that they do not have flat frequency response when the EQ knobs are centered. The built-in voicing is not necessarily the best starting point for upright bass, so it's worth playing with those knobs, and not being afraid of rather extreme settings. For instance, turning the Bass knob down quite a lot will tend to flatten most amps. Everything, including "flat" response, is a starting point, not an absolute.
Amp placement is important. Getting it further away from you will make it sound more natural by reducing feedback. Even amounts of feedback below the threshold of audible howling, affect your sound. It will also change how you listen to yourself in relation to the band.
Every bass amplifies and feeds back differently, so you might find that your bass has a good side and a bad side, affecting the best location of your speaker. For instance, I put my amp on the floor, others on a chair, and so forth.
If you're switching from electric bass, it will take some getting used to the different dynamics, both for you and for the band. They will have to be more mindful of the fact that you're now playing an acoustic instrument. Even if it's amplified, it's still acoustic because the bass is interacting with its own sound.
