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Valve: HDMI Forum Continues to Block HDMI 2.1 for Linux
(www.heise.de)
This is a most excellent place for technology news and articles.
should be able to with hdmi arc, not sure 100% tho but it seems like you could tell the projector where to send the audio, i know you can with tvs and hdmi arc. worst case scenario you do dp in to the projector and hope valve has stereo or optical out to go into reciever