The Bayo IGN maps are rastermaps and like all other rastermaps they can not easily be converted into Garmin format.
I strongly advise you to use the latest Topo France v3 Pro, it's based on the same IGN data (but much more up to date than the Bayo maps which are very old) and is one of the finest Garmin Topo maps you can get.

If you persist in converting .byo maps you should start to convert the ~6000 map tiles into png format with a program called cByo and generate an OziExplorer calibration file. After a few weeks of hard work you can start converting the png files into jnx maps or convert them into Garmin vector maps with Mapwel.