Duvan,
I have a group 5 kit so I can't say what has changed from group 5 to 6, but the main things I can think of that changed from 4 to 5 are the new, adjustable engine mounts, the addition of retaining screws/washers to the gearbox output shaft seal and a shorter exhaust pipe part way through group 5.
I think they also changed the glue used to attach the magnets in the engine pulley starting with group 6 or near the end of group 5 and made a change to the oil pump cover on the bottom of the main rotor transmission which adds cooling fins and recesses the four bolt heads for more clearance with the lower fuel tanks. There may be other things I'm forgetting or am not aware of.
Mike