OK, time to play everyone's favorite critical reasoning and reading comprehension game, "Decipher the Denon Manual!"
Hmmm, now that I read it more carefully I will retract that, I don't think it will touch a 480i HDMI signal at all.
On page 40, in the "i/p scaler" section, when it describes what turning the scaler on does, it states: "Use i/p scaler function for for analog video signal"
I guess that's pretty clear. I don't think it can touch an HDMI input at all. It's a little confusing because I don't see where they explicitly state that no video processing can be applied to an HDMI signal, but they do say that you can't go 720p->1080i or vice versa.... which implies that you CAN go 480i->480p... but I guess this is really just for analog inputs.
So, in conclusion, I take it back, the 1909 will do nothing to an HDMI video input signal.