Cifs and samba are two protocol implemetnations of the same protocol to transmit files. rsync is a tool to move files over file protocol, so it should work here as well. One note of care - be sure to do the moves in small hopps, as you can see in this forum. Dont try to import all 100 GB (or whatever) at once.
Another thought - spend some time analysing your data, maybe you find some things you want to sort out befor import - content types, categorisation, extra import filters for metadata … this kind of stuff
Norgan