Manycam is a popular (paid) software that allows you to use multiple cameras and apply graphic effects or backgrounds and then generate a video stream that can be captured by MB LIVE.
For optimal operation with MB LIVE it is recommended to set the MANYCAM output to 720p 30
and set MB LIVE to capture from Manycam at 1280 x 720 30 fps
MB LIVE only captures video from Manycam, but if you want MB LIVE to use the mixed audio from manycam then you also need to set MB LIVE audio capture from manycam like this: