I am in consensus with all of the previous reply posts. Would be the most practical approach to start with a docked iPad2 MF4, with ability to record/play, though albeit a bit sluggish UI due to the old pad hardware, but can compensate with the comparatively lightning fast response of the remote newer iPad 6.
IME the primary impetus for running MF5.1 on the original DL series would be for the ability to break free of the iOS/Apple hardware choice constraints, and therefore the array and possibilities of UI hardware choice is vastly increased. Though to date I have not connected/updated my DL1608 with MF5.1, I have installed it on a Dell XPS 18" Win10 1080P touchscreen tablet as a proof of concept. Demo mode appears to operate without issue, well the increased screen area is impressive and luxurious. Eventually I expect to have a crack at installing FW MF5.1.