Just create a mpv.conf file next to mpv exe or dll and add input-ipc-server=multifunplayer-mpv line inside. You can do this to connect MFP to any software that uses mpv internally.
The stash repository first tries to use the video filename attached to the stash scene, so you can point the local repository to a folder with multi axis scripts and they will match.
If it does not match anything locally then it downloads the single axis script from stash.