Og33 is right on target. See the HDMI FAQ in my sig for some more details, but Dolby TrueHD, DTS-HD Master Audio, and multichannel PCM all involve too much data to fit across an optical or coaxial digital connection. Multichannel PCM discs have become rare, while TrueHD and DTS-HD have become the two standards. Both TrueHD and DTS-HD contain a "core" track that uses high bitrate Dolby Digital or DTS. This is generally disregarded by TrueHD and DTS-HD decoders (whether they are in a Blu-ray player or in a receiver with HDMI v1.3 support), but players will steer it to their coaxial and optical outputs for compatibility with equipment that doesn't support HDMI audio.

There are quite a few Blu-ray players that include a multichannel analog output. This output lets the player decode the new formats internally, convert to analog, and output that. You'll see quite a few people around here pairing the Model 990 (or the Model 970) with the OPPO Digital BDP-83. That is because the BDP-83 supports decoding of these formats as well as playback of SACD and DVD-Audio. It can then output all of that audio via 7.1 analog into the Model 990 or 970. There are other players with this capability, as well, such as the Panasonic BD80 and Sony S560. What player do you have currently?