You are basically trying to fit a 'round peg' (3.5mm mini-jack audio connectors) for a 5.1 analogue PC sound card compatible 5.1 'surround sound' speaker system into a 'square hole' (HDMI) for digital Dolby Audio compatible TV sets / Streaming boxes and hoping that it can be done with a lot of additional cables / converter boxes and 'Heath Robinson-style jiggery-pokery'.
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You will never get true 5.1 digital surround sound unless you have a AV amplifier / decoder that has SPDIF inputs (from the SPDIF outputs of the TV or Streaming Box) AND 3.5mm mini-jack audio connector sockets for its dedicated surround speaker channels to be output to your '5.1 surround speaker' setup.
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