If you want to easily open audio files from Finder, as Bob has suggested, you can make MediaCenter the default so it just does it when you double click on an audio file. Do something similar to this to set it up:
1. Highlight a file in Finder. Press <command>i (or right click for Get Info) to open the Info Panel.
2. In the lower part of the panel you'll see "open with". Click the currently selected app under "open with" and pull down to "other".
3. In the dialog that comes up, you'll be shown your apps, but you'll notice that Media Center is greyed out. To fix that, just change the "enable" pull down from "recommended apps" to "all apps". Now you can select any app you want.
4. Find and click Media Center. If you have more than one version installed, click the one you want to use. In my case it was media center 28.
5. Now Media Center will open JUST THAT FILE. But you want all files of this type to be opened by Media Center. So, cilck the button right underneath that says "change all". This will assign media center to all files with that type.
You will need to repeat this process for each audio file type that you work with in the file system: FLAC, MP3, WAV, etc. There are probably only 3 to 5 that you use, so it won't take too long.
While I'm a big fan of the Mac in general, I'm not such a big fan of Finder itself. Apparently a lot of people don't like Finder very much. There are quite a few replacements for Finder that do more/better things than Finder. For example, PathFinder and Forklift. I don't use any of these but have played with them in the past. I think I'm going to give a few of them a try again soon. I would really enjoy having a Finder type program with dual panes for easy drag and drop (or cut and paste) of files from directory to directory. That's a very error prone process with Finder and I'd like to fix that.
Good luck.
Brian.