I'm almost certain that you're screwed, dude.
My understanding is that the new digital display uses a totally different ECU than the older monsters have, and that your ECU wouldn't communicate with the older dash at all. Add in the fact that the new gen monsters haven't been out long enough for the truly serious mods to come out, and I think you're on the hook for a new OEM dash.
Sorry that happened to you.
Yeah, I've came to the same conclusion when I tried the start it with the display unplugged and got nothing. I guess I'll put it back together and ride around blind for now.