Question

I’ve installed the correct plugin and software from the Presonus website for my mixer and Mac and still can’t get the two to comunicate.

Answer 1

You need to ensure you are not running Catalina. 

Link: https://support.presonus.com/hc/en-us/articles/360034790891-Apple-macOS-X-10-15-Compatibility-Statement-

Universal Control v1.7.6 installed on a supported OSX will help. Also ensure the drivers are allowed to be installed correctly. 

Answers Article: http://answers.presonus.com/27478/installed-universal-control-system-firewire-devices-showing?show=27480#a27480

Link: https://support.presonus.com/hc/en-us/articles/115005456483-Installation-Issues-with-FireStudio-Series-on-High-Sierra-Mac-OSX-10-13

Answer 2

UPDATE: I got my 16.0.2 (should also work for 16.4.2) working as a 16in/16out audio interface over firewire on Catalina. Turns out, during the installation of the firewire drivers, apple's new security features disable the drivers on installation, with no warning!? 

You'll know if this is the case if you follow these instructions:

https://support.presonus.com/hc/en-us/articles/210047233-How-Do-I-know-my-StudioLive-is-connected-to-my-computer-and-functioning-over-firewire-

Also, if you check on your StudioLive 16.0.2 firewire mixer System Menu >> "Page 3: Digital" the status will say "no driver" if the driver has been disabled.

To check for disabled software, follow this answer (it says OS X 10.13, but works for 10.15):

https://answers.presonus.com/27478/installed-universal-control-system-firewire-devices-showing?show=27480#a27480

To rectify, follow these instructions (again, it says OS X 10.13, but works for 10.15):

https://support.presonus.com/hc/en-us/articles/115005456483-Installation-Issues-with-Universal-Control-on-High-Sierra-Mac-OSX-10-13

Won't get UC working, but will get your mixer taking to your computer. Hope this helps!