I can't say for sure and do not have so huge practical knowledge as JH, but it seems your goals are not feasible to do.
In nowadays market there are a lot of receivers which do the DAC brilliantly. On the other hand - the bitrate (and so - frequencies) of the modern digital links (HDMI stream, for example) are approaching 10Gbit/s and even more. At this frequencies the DIY gear just does not seem to work.
The second consideration - is parts' base. Even Chime was used ICs for DAC. The proposed device will have to use ICs available to the buying, so the chance is very small to get audiophile core. Several technologies use some kind of coding, which raises questions about supporting a great number of music signal sources.
While SPDIF in its modern state allows to deliver 2 channel of 192 kHz/s bitrate it lacks supporting of enough bit-depth (up to 20bit only), so this kind of device will be even more limited.
I do not speak now about fully built devices, which can be factory-built by JH ideas. This is feasible.