Don't know, and a buddy box does not have to have the same capabilities as the master just the same brand. Buddy boxes typically are non computer 4 channel radios.
Here is a compatable box for all Spektrum radios (according to Horizon anyway) http://www.horizonhobby.com/Products...rodID=JSP98140
Another thought? It may be possible that the trainer switch on his DX6i is not working?