Wow, they look pretty impressive-- "infinite" polyphony, T2L technology, and a combination of sampling and modeling! Either model should certainly work fine as a MIDI controller, in addition to being a digital piano.
My only thoughts about using it as a MIDI controller is that it doesn't have many controls the way that most dedicated controllers do-- but you should be able to buy a separate mixer-style controller to use with it if you need more buttons and dials and faders to fiddle with.
I looked specifically at the J7 combo. The board had limitations to what I need. I wanted to play the lower organ manual from a second keyboard via midi and you can't. The Leslie on fast speed sounds hideous. The piano has a bright attack to it that needs work. The electric pianos are middle of the road. The other tale telling sign is that musicians aren't flocking to the keyboard and it is a little pricey as compared to its competition. My two cents which is about all my opinion is worth.