I see the devices out there: those products that supposedly take an HDMI signal and convert to USB, or vice/versa. There are even direct cables for doing this.
Here’s the deal, are there any inherent problems in doing taking HDMI audio (let’s say DSD256) and sending it to a USB input in a DAC, for instance? Degradation in quality? I wouldn’t think so, since digital is digital, but hey, I’m not an expert. I just have an opportunity to “tinker” coming up, so I want to get some opinions of other tinkerers. 
Actually, I think the concept is a sound one. I was bequeathed a Marantz SR7012. It has USB input, as well as an Ethernet input, so I should be able to go into the box, use room correction, and then out of the box via HDMI without a AD/DA conversion. The unit handles up to DSD256, but perhaps that’s only with AD/DA conversion. Well, anyway, yeah, I’m tinkering. Heh.
Nick
A few important points…
HDMI supports a max of DSD64 – unless the standard has been updated for higher rate DSD, and I doubt that.
AVR HDMI output is for video, maybe audio passthrough. You will not get processed audio via HDMI output.
DSD is incompatible with digital processing, such as room correction. Digital processing requires conversion to PCM.
AVR USB input probably is not asynchronous.
Long story short, what you want to do will not work.
AJ
Not even DSD over DoP? Hmmm… Curious things to muse on. Just when I thought I might tinker, I took one to my thinker. So, DSD converted to PCM only.
I have been trying to figure this out too. I want to output HDMI audio from my oppo SACD player but I think HDMI can do native DSD as I asked Oppo people but the problem is that the receiving end may not take DSD if it does not have HDMI input. Byrson DACs have HDMI input now and would work but what 's the point, Byrson is also using signal Delta DAC chips, same as Oppo. It seems if you try to convert HDMI to USB it will automatically transmit as PCM, as I think all the converters I see are for video+ audio and won’t handle DSD, probably not even DoP, though I could be wrong. If they send as DoP, the at least when the DoP signal arrives at the DAC end it can be read as DSD. But I think I asked Oppo and the answer is that is the same - becomes PCM via USB, I think you need to pay a patent fee for HDMI audio for DSD transfer due to the Sony copyright. Transfer via I2S seems less strict but that is another story…
I have done SACD HDMI output from the UDP-205 as DoP with a “de-embedder” - a device that splits out the audio from the HDMI. In my case, that was to digital coax and TOSLink optical fiber, not USB. Perhaps there are comparable options for USB.