Yes, for the PS3, the only way to get 7.1 LPCM (or any LPCM I believe) would be via HDMI. Lossless will not pass via optical or coaxial. For other dedicated players, some (most?) do have built in decoders so you can connect the 7.1 analog outs from the player to any receiver with a 7.1 input and get the full benefit of 7.1, but the PS3 does not have multichannel outs, thus HDMI must be used for TrueHD and DTS-HD.
For standard DVD, 6.1 is the max (DTS-ES, DD-EX), but that is processed and played back in 7.1 if that is how you have your system configured. These forms CAN be passed via optical or coaxial connections.
Sorry, not familiar with the DG800, so it will depend on the version of HDMI it comes with, which I believe is not 1.3, and I am not sure if 1.2/1.2a supports lossless or not. I believe I read here that it does, but can't say for sure.