When you set the OPPO to output LPCM, then the player is doing the decoding and the receiver only sees multichannel LPCM. Therefore, the receiver doesn't get a TrueHD or DTS-HD bitstream - it won't report decoding those (because it isn't) and it will have no way of knowing if the incoming LPCM signal was ever in one of those formats. There is nothing wrong with this arrangement, and you are losing nothing.
If you really want to see your Denon decode the formats, set the HDMI Audio output on the BDP-83 to "Bitstream" instead of "LPCM" - but using "LPCM" does not hurt anything. If setting the player to Bitstream doesn't work, check to see that "Secondary Audio" is set to "off" - having it turned on will prevent a player from being able to output the raw bitstream because it must be able to integrate secondary audio streams (menu sound effects, etc.) into a decoded LPCM signal. The BDP-83's quick setup wizard automatically disables secondary audio for this very reason when you select the "Advanced" audio mode that is intended for use with HDMI v1.3 receivers that can decode the new formats.