Not sure what you are asking. Replacing the audio source file in the project window or timeline? How does your art "react" to the audio? Expressiosn? Something else? You need to explain better. I also get the feeling that you assume you could simply change a "master" layer in the parent comp and it wil magically change the child compositions, which with AE isn't the case.
Thanks for the reply. Again, sorry for not explaining properly as I'm very new to the software. I'll try to explain better what I'm doing and what I want.
Over the weekend I made 3 separate files in AE:
1) a glitch introduction using my logo (the logo moves around and does some glitch effect)
2) a pulsating logo that pulses to the beat (sound keys effect) of a song (song clip #1, 20 seconds long)
3) a particle ring that reacts (audio spectrum effect) to the beat of a different song (song clip #2, 30 seconds long)
I want to take all 3 of these files and put them into a single movie (I don't know the proper terminology yet but I want all three of these to go into one file so I can upload it to youtube, using a different/longer song) so what would be the best way to merge all of these and get the compositions to react to the new audio becuase I can't figure that out. I want to later just be able to almost drag and drop new songs into this 'template' and quickly link the effects up to the new music. I hope this makes sense.
what would be the best way to merge all of these and get the compositions to react to the new audio becuase
You can't, because in AE's way of thinking you still have three separate source itmes for the audio, each with its own in- and out-points and by way of usage in the comp, their own effects and settings. You can of course combine them by simply importing the projects and sequentially arranging the comps on the timeline, but you still have to go in and replace the audio every time. Without some restructuring effort this will not change. You could facilitate the process by replacing the audio with your new audio snippets before importing and then a File --> Consolidate may exactly do that and leave just one file which you can then easily replace with a right-click, but other than that I would first merge the visuals and then spend some time on polishing up the audio usage by adjusting the references to point to the parent comp. A lot of trouble can already be avoided, by dumping the audio in pre-compositions and use those instead of referencing the audio files directly. That way you only have to replace the audio in one place, regardles where the pre-comp is being used and how many times. Again, the issue will be the structure of the project and you have to work on that.