SurroundByUs.com

As I said, optical/coax can only do two channel, unless it is DTS or DD encoded.

"S/PDIF can carry two channels of uncompressed PCM audio or compressed 5.1 surround sound (such as DTS audio codec or Dolby Digital codec); it cannot support lossless surround formats that require greater bandwidth"

You need to encode your audio to DTS or DD, or, to play LPCM, you need a more modern player that can put out spam 5.1 from LPCM, or one with HDMI and connect to something with an HDMI input, that can play LPCM. There are HDMI Audio extractor/De embedders, that can play 5.1 or a few that can play 7.1 but read the reviews etc.

Yeah there is actually the ADAT format, that can carry 8 channels, was popular in pro audio gear, but never used for consumer.

Modern players do LPCM over HDMI. For me, the state of HDMI for consumer is frustrating because the spec says up to 32 channels, but there are no drivers or receivers that go beyond 8. This makes it difficult for those up-remixing to immersive formats, like 7.1.4 etc., at least for live monitoring of the mix.