[sleestack1]

Is this fixable?

For instance, DISCSUBTITLE won't pass into the database from a DSF file.

It will pass from most other files (FLAC, MP4, DTS)

If its not fixable, is there an alternate container that DSD should be placed in so this info will pass through?

[Sylfest]

Try SETSUBTITLE for dsd files same with MP3.

[HeresJohnny]

DSF files use id3v3 or od3v4 tags with the added caveat that id3v4 tags may not be processed correctly by all applications. I would recommend to convert/pack DSF files with WAVPACK, for example via batchencoder (be sure to tag your DSF files with id3v3 tags if you want to keep most tags during the conversion process). Not only will this save you tons of space, the WAVPACK format also uses APEv2 tags which may be more familiar to use.