Not sure what OP is trying to accomplish, but title of thread suggests OP's trying to send audio to TV via RCA. I think OP wants audio from his new TV to go through his $8K stereo to achieve sound superior to that of the TV. If his $8K stereo can convert digital to audio but lacks HDMI, perhaps a device like that suggested by RW might work If his $8K stereo cannot convert digital to analog, he needs an external DAC.
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