Facel, seems like you're making things complicated for yourself. Things don't need to be complicated by using the right tool for the job.
The requirements you describe i.e. playing video to a display whilst outputting audio to a DAC and having a built-in DLNA server is all doable with Kodi, you also already have JRMC on a NUC so you could use that (although many would argue that Kodi makes a better media center than JRMC in this day & age).
Instead of trying to use a music player to play unsupported video formats, just use an AV media center.
You can use Libreelec on your Pi or on your NUC or install Kodi on your Shield (although Libreelec could a more complete solution with regards to running Kodi).
The requirements you describe i.e. playing video to a display whilst outputting audio to a DAC and having a built-in DLNA server is all doable with Kodi, you also already have JRMC on a NUC so you could use that (although many would argue that Kodi makes a better media center than JRMC in this day & age).
Instead of trying to use a music player to play unsupported video formats, just use an AV media center.
You can use Libreelec on your Pi or on your NUC or install Kodi on your Shield (although Libreelec could a more complete solution with regards to running Kodi).
