Really sorry about not getting much of an update this weekend, got a bit busy and then last night was watching a hidef movie!
The Denons definitely have a problem somewhere with HDMI - I did get the 3910 working thru DVI, with an adaptor cable (I forget offhand what I set the Vantage HD to in the "HDMI Audio Settings, but it's in a previous post).
The auto-switching (ie outputing 50 or 60 Hz, based on the timing of the input) has started working now. It is possible that I rebooted the VHD at some point after I set it to "Auto" and that this caused the setting to take properly. It wasn't consistent in the beginning, but I can honestly say it always switches now.
The "locking in" of an input, and then producing an output DOES take a few seconds, so I would say it is a bit slow to identify and lock, but it always gets it right. I have tried it with various devices at various resolutions and it hasn't put a foot wrong yet.
I even tried it with a Sony Hi-def video camera, outputting component at 1440 x 1080i, and it got it spot on.
Sorry, I didn't try the "repositioning" thing yet, but I'll give it a try this week.
Overall, I would say the deinterlacing and scaling on the Vantage HD have been superior to anything else I've seen. This is what I expected (and why I ordered it) so I am pleased. The image quality is also very good.
The only problem left that I haven't solved is that the picture adjustment settings (ie contrast, brightness, sharpness, color, etc) sometimes "stick". I.e. when I go to the Sky Satellite source from the DVD source, the settings remain as they were for the DVD input, instead of switching to those I had set for the Sky input. If I pull up the menu, the settings are all showing the correct values for the Sky input, but the screen clearly reflects that the device hasn't actually used those settings. If I then make a one-increment change to any of the settings, they all suddenly "switch-on" and the screen changes to reflect the settings.
It's really not a big problem once you understand it - no doubt it'll be a simple fix when there is a firmware update.
Everything else is brilliant.