They have Lightning jack mixed with other rabbit but to my knowledge there is not a Sound known as LJ duet.
Foxpro will custom mix two sounds for you or if you buy the proper Foxpro Ecaller you can play two sounds simultaneously as long as both speakers are turned on.
My Fusion has an External speaker so I can play two sounds at once but on my Krakatoa I cannot as I only use the one main speaker.
"Anyone taking up handloading necessarily plays with unknown factors and takes chances. But so does anyone who drives a car,goes to a cocktail party,eats in a restaurant,or gets married."
Jack O'Connor 1963