Thanks very much for reply,the sound output in my bubblegum96 is now works corretly.
There is a small episode that I can not login system when I prepared to solve this problem.
The detailed information is the following:
1,Plug in power to the Bubblegum96 board
2,There first shows an dialog with username and password input（Factory developer says that is lightdm）
3,When I input correct username and password,it always inform me that password is incorrected.
4,On the upper right corner is windows manager selection with options of "Default Xsession,LXDE,Linaro,OpenBox"
5,On another computer use ssh to login bubblegum96,it not shows incorrect password and all operation is normal.
Finally,I reinstall the debian system with sd card image,sound output in this version is works corretly.