In case of doubt, it's probably a safer bet to use a stereo connector and not connect the ring to anything.
A mono connector is basically a stereo connector with the ring and sleeve connected together, and if the Sony has any problem shorting the "ring" position of its jack to ground, then a mono connector won't work.
It's genius to find that the IR connection works when the plug isn't inserted all the way. It often takes genius to overcome idiocy like that.
A good answer is easier with a clear question giving the make and model of everything. "The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
