Guess the bottom line is what sounds the best. Seems as though imaging is out the door when you don't have dedicated seating and dealing with the great outdoors. Personally I like to hear the seperation we get with stereo, but I'm going to try a mono system so I can hear it for myself.
Do you just use some type of mono converter? The only one I've seen is made by O.W.I. Or maybe the product by Audio Plex would be the best bet. It's a volume control the turns stereo into mono, which allows for the rest of the system to play in stereo. Sounds like the best bet, then it could be changed with minimal expense and labor if not liked.
CMack