Re: compress dolby or dts output over optical cable?
Yes I'm sorry to say you're going about this the wrong way.
Darryl went into detail but basically no you can't do what you're trying to. Your headphones are designed as a consumer end-use product.
You'd need to get a proper interface with 6+ outs with monitors to match. There are virtualization plugins to emulate surround monitoring on headphones but if you aren't experienced mixing in surround it's not helpful. You are staring down a very deep rabbit hole.
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~Will
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