If you need both possibility, to stop/play particular sound and stop/play some groups of sounds then you need to tag each file distinctly (each sound should have unique tag/name). With this you are allowed to stop/play a particular sound.
Now to be able to manipulate groups of sounds I would create a function in which you can put actions to stop them playing one by one. For example
Function On "stopMusic" => Audio Stop "sound_1"
Audio Stop "sound_2"
Audio Stop "sound_3"
Audio Stop "sound_X"
Or if you name it with some assumed format like above "sound_x", then you may want to do some more clever thing like:
System -> For "stopMusicLoop" from 1 to maxMusicIndex => Audio Stop "sound_" & loopindex
So I would suggest something like this. There is no way in C2 to stop/play music and sounds separately.