Below you can see how I partially solved my search for a “closed system” DS. The OPPO 105D is linked to DS via River Cable Gold Signature SPDIF. The 2 x 4TB Samsung/Seagate HD’s are direct USB into OPPO using AudioQuest Carbon USB 3 cable. I also use the OPPO105D (a true Universal player) as a Transport. For SACD play, the OPPO has its own analog outs into the CJ Act2/Series 2 Preamp.
Of course, this only partially solves the problem. Since SPDIF cannot carry DSD, I do have to stream that library which is also housed on a 3rd Samsung/Seagate 4TB HD.
DSD HD>PC>JRiver 19.146>Pangea Ag USB>DS.