I've been told by our flight training director that his 6EX 72Mhz radio requires another Futaba computer radio to buddy box with.  I own a Futaba 7C 72Mhz radio and a standard 4YF buddy box, and my 7C buddy boxes with it just fine.  I don't know why there is a difference, only that I've been told there is.</p>

I'd explore the Futaba 6EX manual for further information:</p>

http://manuals.hobbico.com/fut/6ex-2_4ghz-manual.pdf</p>