I just went through this with my DTVPal when I hooked it back up. Denons and Marantz are a little weird. While you may have it set to auto in the receiver settings, you still need to hit the movie mode on the remote. If the signal is broadcast in 5.1, it will switch to surround and you should not need to do the setting again.
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Samsung UBD-K8500, Panasonic DMP-UB900 -> Yamaha CX-A5100 -> Sony XBR-75X940C; Mediabridge 6' and 15' HDMI cables.