I do use 2 of these. I followed the directions in this thread. See post 30 [EDIT] step 5 for dipswitch settings the version number of the FMC doesn’t seem to matter I have version 5 I think. Also, see post 8 regarding gigabit.
You could use an ethernet switch between your FMCs and the bridge and it would solve the mismatch of speeds if you wanted to keep your FMCs.
I use Roon to control my music, but Mcontrol works too.
I am not sure about the Force and Auto settings. I did this about a year ago or more.
If post 30 doesn’t help I can crack open the aluminum box that I mounted my FMCs in and see the settings, its a bit of a pain to reach it, but I am happy to help.