NOT INTENDED AS AN ANSWER -- JUST GETTING CLARIFICATION
I am having a similar issue, however, to clarify your question - do you mean that when you set the PreSonus Universal Control to Multi-Mode, that you do not see these audio channel pairs in your macOS > Preferences > Sound settings?
Because, I do see these, but they are not available to me in PT as I/O on an AUDIO track.
The documentation I could find about the PreSonus IO24 interface, states you have to use an AUX track, which I have not yet tried, so if you have tried the AUX method let me know.
Screenshot of macOS Preferences Sound (from manual) -- (I tried to copy/paste the image which may not work)
Source: User Guide A—8.5X11 (presonusmusic.com)
