@resolution: I’m not surprised hardware media players have strange/arbitrary limits on MKV containers. If it helps, I know Blu-ray discs can have up to 32 audio streams, and it’s possible an M2TS container may work better even without being burned to disc. Careful with your counting, though – some authoring tools (tsMuxer) allow you to add more than 32 without any warnings, and disc behavior with too many streams is bad.
Thanks, I hadn’t thought to try M2TS on the Oppo. Will have to experiment with that sometime.