Beckhoff maintains to sets of DDs for its Bus Coupler devices. The newer one and usable in third party engineerings like SYCON.net are tagged with MDP (Modular Device Profile). When unpacking the file referenced above, find a subfolder "Beckhoff_BKxxxx (MDP)" which contains MDP version of couplers' descriptions and Modules XML in further subfolder "Beckhoff BKxxxx MDP". Thus, for SYCON.net we need "Beckhoff_BKxxxx (MDP)\Beckhoff BKxxxx MDP.xml" and "Beckhoff_BKxxxx (MDP)\Beckhoff BKxxxx MDP\BKxxxxModules.xml" to be imported as EtherCAT XMLs.
I would recommend that previously installed XML file "Beckhoff BKxxxx.xml" is removed from the installation (on Win 7: "C:\ProgramData\SYCONnet\EtherCat\DDF\Beckhoff BKxxxx.xml") in order to reduce the devices number in the catalog with many confusing entries for BK1120 e.g.”