The only difference between the 2 models is that the Mark II has an etherCON port for the MFC connection while the original Axe-Fx II has an Ethernet port for the MFC connection.

The Ethernet port on the original Axe-Fx II

The etherCON port on the Axe-Fx II Mark II

etherCON uses an XLR-type barrel that surrounds the actual RJ-45 connector; this barrel will lock into place just like an XLR cable can, which is much stronger than the tiny plastic tab that secures a normal ethernet cable.

Note that you can still use a normal ethernet cable with an etherCON jack on the Axe-Fx II Mark II (or the MFC-101 Mark II and Mark III). However, you cannot use an etherCON cable with a standard ethernet port like on the original Axe-Fx II (or the original MFC-101).