Flying Fox wrote:2-channel over optical is for PCM (uncompressed) format.
If your media files compress+encode the audio in AC3/DTS (up to 5.1 channels) already, it is possible to configure media player software to bitstream that audio directly to the receiver and the receiver handle it. Of course Windows default won't do it for you. You need apps like AC3filter and MPC-HC.
I must get my pedant on, please excuse me. Your explanation was valid enough, and probably addressed the question, but I wanted to clarify and expand a few parts.
2 channel over optical is for 'live' aka uncompressed streams. Some newer devices can output uncompressed multichannel, but the majority do not.
If your media files contain precompressed audio (AC3/DTS/multichannel AAC/etc), those precompressed formats can be transmitted to the receiver/decoder digitally, with the source device (PC) only demuxing the compressed audio out, not performing any decode or processing.
"Bitstreaming" is a somewhat confused term still. Some folks seem content to have it mean "digital, not mangled, output digitally", others further specify that it should be the exact data that was stored on the disc with the video, and some feel it means "output along with untouched video, HDMI-style". I personally like some of the former and some of the latter. I only use "bitstreaming" when referring to HDMI output of unmodified compressed audio. Your choice, though.
Please don't edit my signature for me. Thanks.