How do I twirl open multiple folders in the Finder?

I have a main folder. Inside of the main folder are 55 folders. Inside of EACH of those 55 folders are two files: an audio file and a video file. I need to copy all of the audio files to another drive. What I want to do (in my main folder, in list view) is twirl open all 55 folders, select all 55 of the audio files, and copy them over to my other drive.

Is there a way to do this? Or am I just going to have to manually twirl open each of the 55 folders?

(I'm at work, where I'm using Mountain Lion on a Mac Pro. But I have Mavericks at home.)

(And, yes, I'm aware of the irony that it has taken longer to submit this question than it would have taken just to manually twirl open each folder, which is what I'm going to do after submitting this. But knowing the answer to this will be REALLY good to know for future reference! Thank you.)