Just to be sure, can you please tell us if you are playing to the Oppo player via an HDMI input or via UPnP / DLNA ??
If the former (HDMI), then its audio input specifications (
https://www.oppodigital.com/blu-ray-bdp-105/blu-ray-BDP-105-Features.aspx ) are Dolby Digital, Dolby Digital Plus, DTS, AAC, up to 5.1ch/192kHz or 7.1ch/96kHz PCM -- but there is no mention of DSD / DFF support
If the latter (UPnP) then its claimed audio input capabilities include PCM L16, FLAC, MP4A, AIFF, WAV and MP3 -- but again there is no mention of DSD / DFF support.
So, if you find that the player does play DSD/DFF then it is perhaps more by chance than by design. And perhaps not surprising if it does not always work.
Furthermore I am actually not sure if MC is even able to split DSD/DFF streams into track based sub streams based on cue files when pushing via UPnP. It sounds quite unlikely, as IMO it would need to convert to PCM to do the split, and then convert back to DSD/DFF.
So I think your best bet is to set MC to Always Convert audio to PCM L16 (No Header) although possibly PCM WAV (With Header) would also work fine.
And by the way, apropos the side comment about 5.0 channels, there is nothing either in Oppo's specifications or in its UPnP declarations which would make you think that it might be able to play 5.0 (it declares 2ch over UPnP and 2, 5.1 and 7.1 over HDMI -- don't be confused by the "up to" statement because the PCM standard specification itself only permits 1, 2, and further even numbers of channels 5.1, 7.1, etc. upwards)..