I am not familiar with Mac Family Tree Maker(MFT)but in GEDCOMs the XREF of an individual is found in the FAM record and the XREF for the family is found in the INDI.
0 @I1@ INDI
1 FAMC @F2@ <= Family where individual #1 acts as a child.
1 FAMS @F1@ <= Family where individual #1 acts as a spouse.
0 @F1@ FAM
1 HUSB @I1@
0 @F2@ FAM
1 CHIL @I1@
I only say this so that you are sure that you set it up correctly. I am told that a program called GEDCOMit may be of help to MAC users. It only works on MAC, I'm a PC :-D