RIGHT I had a different post, but I had to eat my words.
I've figured a workaround after some trial and error. I downloaded the latest Winamp, configured Milkdrop with the dialogue provided, then I copied the milk2.ini and replaced (after backing up) Musicbee's version. That also gives the benefit of exposing all of the settings available in the .ini file itself.
The settings I used in Winamp were to set Desktop Mode onto the second screen and force start upon opening the visualiser. Then after copying the .ini and opening Musicbee I started running the visualiser and it worked, though Musicbee wasn't responsive as the visualiser takes priority so the controls don't function. To fix that, I right clicked and chose Musicbee's desktop mode and it enables me to use the full window on the first screen.
There's some other strange behaviour happening, such as not being able to access my main screen desktop, but doesn't really matter as I can alt+tab to other programs and still use MusicBee's main window. Overall I'm quite happy for now!
Cheer Steven, I'm exceedingly grateful of the power and flexibility of what you've created! Thanks!!