Disappointing- but thanks for experimenting.
I have now tried this. I converted the 24/96 flac file to 24/97 wav, 24/48 flac and 24/48 wav. The 24/96 flac plays but with the strong hiss. The 24/48 flac plays with no hiss. Neither wav file will play at all but rather both resets the player when it tries to play them. This was with firmware 0.20. I then tried to upgrade to the latest firmware 0.21 but the results were the same. So the conclusion seems to be that there are problems decoding some 24/96 flac files (confirmed by Fang), that downsampling to 24/48 does not have this problem and that the player is unable to play hires wav files.
Btw. the same 24/96 wav file plays without any problem on the Colorfly C4 however the C4 does not play hires flac.