Yeah DQX SCDs are a little irritating, it fully interleaves mono DSP files, including the headers. vgmstream's current implementation of interleaving is too "smart" (assumes to much) to support this directly, so I'll need to either put together another layout or do something with virtual files like for AIX, which is almost the exact same situation but with ADX instead of DSP.
The stuff I put in earlier is just to handle the SCD header used in the DQX, which elucidates a previously unknown value.