Ive got one installed and i havent yet seen a pro mode on it...its got a lot of features on it and i dont have a lot of time to play around with them...
Pro-Mode, when enabled, turns the outputs into highs/mids/lows instead of front/rear/subs.. it's utilized by people who bi-amplify a set of components in the front, don't use rear speakers and have a set of subs.
The 860mp has pro-mode, but I don't see it on the 780.. if it has it there'll be a tiny switch on the bottom of the stereo for it..