In the Advanced menu, there's a submenu called "Graphic Channels", where you can see what channel is active, and select the channel you want. There are 15 channels to choose from, where channel 1 is the default.
To select a different channel, just pick it from the menu, or, easier than that, you can just hold the control key and use the numeric keypad, 1-9 and shift 0-5 (shift adds 10 to the number you press).
For example, on some discs, there are multiple languages in a single song. English may be on channel 1 and French on channel 2. To switch from English to French, just press the control-2 on the numeric keypad.
The channel number you prefer is saved per song, not per singer, so if one singer changes it in their list, it changes for all singers. Let me know if this is not what you want.