I have the 6EX 2.4, not the 7C that you have but I think the connectors are the same, square one on the 7C and then whatever the buddy box has (I have used buddy boxes that were round connectors and some with square connectors), just have to have the proper trainer cord. One thing to note, as the instructors passes control to the student (buddy box) there is a noticeable delay between the time he turns control over to the student (about half a second or so) but; fortunately, when the instructors takes over from the student, the transfer is essentially instantaneous.