I just talked with Apple support. There isn't a way to downgrade back to 10.15.4 unless you have a Time Machine backup from prior to the update. If you do, you can restore from that backup following these instructions: https://support.apple.com/en-us/HT204904
Unfortunately for me, I'm on a brand new laptop that came with 10.15.5 and I don't have a clean backup to restore from. It sounds like I have no option but to wait for Presonus to update the driver. I hope it's fixed soon.