I'm no expert on Flac but over on the iBasso DX100 thread there have been some similar issues raised and there is mention of improper tags and some suggestions of how to fix. Maybe worth you looking on this page...
As far as ICS sound quality, I didn't use 2.3 for long at all, but I am quite satisfied with the SQ after updating. As I also have a DX100 to compare to, I personally can't complain about the Z. It may not have the dynamics or output to drive higher impedance HPs of the DX100 but it's not a mile behind either. There are similar variable opinions about the SQ of the various FW versions of 2.3 on the DX with some reverting back from the latest version 1 or 2 releases. I'm staying with the latest versions on both devices.






















