All the ones I have done to date were McQuay RTU's with the MTII boards in them. We simply added ethernet cards to the RTU's (McQuay charges a LOT for JCI ethernet cards BTW) and connected them Bacnet IP. Look at the MIG(s) and see which template file they are using. You should be able to reverse engineer how to connect to an FX-60 with that info.
If sense were so common everyone would have it !
Any advice provided is worth exactly what you paid for it, not a penny more not, a penny less !!