Hi Andy and yes like PaQ mentions if you're transferring into Modo I'd recommend LWO format and not OBJ - the data in LWO is the closest to how Modo structures things internally itself and so its LWO importer doesn't really mess around with stuff. Modo's OBJ importer has improved in recent releases but still kind of has a ways to go with handling n-gons.
Indeed, it looks like double sided materials are my best option at this point. I was hoping to avoid them since I have had trouble with them in Max, but I think it's the only way I am going to get these models into Max.
Hi Andy - for going into Max your best bet is probably exporting to FBX format out of MoI.
If you need single-sided lighting, then it is possible to use the Flip command in MoI to flip pieces that you need to have reversed before doing the export.
But for regular renderings just using double sided lighting should solve the problem without any extra messing around.