I'm having similar issues with a FiiO X3. It worked OK with 7.0 (some strange noise artifacts), and works when I run speakertest in 7.90 over ssh. If I select the FiiO from within kodi in 7.90 audio is still send through the default odroid HDMI output.
Here's the log file with verbose logging for the audio subsystem.
EDIT: I switched from FiiO to default and back to FiiO within the logged session.