It will downscale to 720p or interlace to 1080i. I would assume that the 1080i will be correctly flagged so that a processor or source display can convert back to 1080p24 but I've nothing with 1080i film mode detection to test (until Lumagen get it put on the firmware and I swap my DVI for a ProHDP anyway!).
My Snazio has kicked up on GMC??? A gmc encoded divx or something. Was just me trying to watch some of my mates hooky family guy episodes so wasn't bothered at the time.
Oh and if you don't have WM9 decoding on your AV amp you will need to do a 6ch connection for any WM9 HD files.
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Top Gear in HD - my two favorite things ever finally combined!!