Internal means internal to MFP, it is used to play funscripts only without a video.
Easiest to setup is mpv, if you try to connect it MPF will prompt you to download latest portable version to the bin folder next to MFP executable.
Otherwise yes you have to install/configure one of the other video players.
You probably mapped the vibe to L0. L0 has a default position of 50% so it sets your vibe to 50% strength by default.
You have to use V0/V1 which have default value of 0%.