Let me try to address these things:
1. When the screen is off, the buttons are locked. You have to depress the power button (shortly) or the return key to turn the screen back on and unlock the touch buttons. This is intentional.
2. I had not really noticed this issue until you mentioned it. I find that when I am playing mp3 files, I can rewind all the way back to the start of the song; when I am using FLAC files, I can rewind all the way back to 0, but then it will automatically skip back up to 10 seconds on the song. I have not tried this with WAV files yet. This is most certainly a bug in the firmware, because the same thing happens with my 770 and 800 players. Xuelin has traditionally had problems with FLAC files (in one way or another), so hopefully they'll eventually get this problem sorted out...we can hope, at least...
3. Sorry, I don't really use shuffle mode, so I really can't help much here, but I think this is how the firmware was set up, so Xuelin may not consider this a bug...
The sound differences from the HOs on the new modified 770C are not as apparent as they are on the 770 and original 770C (with their more original firmwares). The Dark is supposed to be more neutral and the vocals are more recessed. The Bright has "amplified" bass and treble and the vocals are more forward. With the firmware on the modified 770C, the power thru the HOs has been more governed, so the difference between the 2 HOs is not as striking. I guess you would have to listen to the 770 or original 770C with their original firmware to really appreciate the difference.