It is a problem of the HDMI standard. It is only designed to pair with licensed equipment that has paid the HDMI consortium. There is no way to break-out analog input directly into HDMI. The HDMI processor on the receiver needs to handshake with a stream that has the proper flags saying "hey, I'm from a device that paid you to use your system". The only outboard solution that comes to mind is a production workaround with over $500 of boxes. One could use a SDI audio embedder to a converter SDI-to-HDMI. There would still need to be a video signal as the handshake will not happen without it. SACD probably uses black video. I have seen a converter that generated its own black for audio-only but it was over $1K. At work we have two suitcases of converters/distributors for SDI, HDMI, composite, etc. for field production, but no multichannel stuff (although SDI carries it).