I dive with a Vytec and twins and no, you can't have two transponders communicating with one unit.
I have the transponder off the main first stange and a pressure gauge on the seconday first stage. I tend to use the Vytec for my main gas monitoring and keep the gauge out of the way until (if) I need it.
Of course, the transponder isn't much use for when you switch to a deco stage and things have been complicated by me moving to a VR3 so my Vytec transponder is probably going to be relagated to my holiday kit and I'll have to hope Delta P bring out their one for the VR3 soonish!
