Hi i bought the RX8 one week ago with a stock mp3 player on board.
However i have yet still not found how to change folders, as i can read only the first folder's mp3.
Thank you...

 

Use the disc up and down botton...

I am not sure how your folder arranged. I think they read:

Say:
Root
|____ folder 1
|_____ Subfolder 1a
|____ folder 2
|_____ Subfolder 2a
|_____ Subfolder 2b
|____ folder 3

Correct me if I am wrong:
The disc up and down will change playing the folder 1, 2 or 3.
It will display as CD1, CD2, or CD3.
The song will play in the folder 1, 2, or 3 first - then going into subfolders. (Oh actually play the root first)

I guess the best way to arrange song is to put them in folders only - not subfolders - since I don't think you can get into them with a few presses of buttons.

But them all in the root! Suffle them and you have non-stop randown music! All 700Mb of it

 

1, it is very slow on reading sub-folders, I just put the songs in their own album folder and that's it.
2, based on how you burn your disc, there is some kind of ransomness to the order of song being played. It is best to number the file name of the song in order and not the ID3 tags to ensure play order.
3, Yes you forward your folders with the disc forward and the next song with the next track button. However, the next track button will NOT skip to the first song in the next folder and it will cycle back to the first song in the current folder. Yet if you let the last song finish playing the player does go into the next folder and start playing the first song in the next folder... odd.