I agree it's probably a VirtualBox issue. What I did on VirtualBox running under Linux was, under VirtualBox/settings/serial ports, checked "connect to existing pipe/socket." Then below that you'll need to enter a device from your OSX machine on the line that says Path/Address.
Hope that gets you pointed in a helpful direction; no doubt there will be better guidance on a VirtualBox forum. Good luck!
--N4VU
Finally bought a license for ProScan, have it installed in a W10 instance within a VirtualBox instance on OS X.
With my BCD436HP attached, Sentinel works fine in that it can see the uSD card in the radio and do whatever I want to do to the card (read, write, whatever) but Sentinel has no virtual controls (unless there is a magical secret menu somewhere that I don't know about!).
Likewise, Freescan will see my BCD996XT (via a USB/RS-232 adapter) and (P2 direct USB) no problem.
But while ProScan can "see" the serial port (when I have the BCD436HP in serial port mode) and will even say "in use by this instance" in the comm port dialog box, nothing happens. Am I missing a magic "go" button? Yes, I have the Uniden serial port driver installed.
Now, if I reset the scanner to "mass storage" mode, ProScan can see the uSD just fine and read and write to it (proving that there is connectivity to the radio through that same USB cable).
What am I missing? Has anyone had this issue and solved it? Not really a ProScan issue but probably VirtualBox ... so ... anyone? Bueller?