The access the additional 8 channels, you go into the FUNCTION menu, and once set up properly,there will be a new sub-menu on the channel assigned to run the MPDX-1. When you open that sub-menu, you can assign a control input to each of the 8 channels on the MPDX-1. There will be similar sub-menus on other programming funcitons, e.g. servo reverse, ATV, etc.

Take a look at the MPDX-1 manual online on the Futaba website: [link=http://manuals.hobbico.com/fut/futm4158-mpdx1-manual.pdf]http://manuals.hobbico.com/fut/futm4158-mpdx1-manual.pdf[/link]