Theater View would be a fine interface for that kind of application. You might even want to create a custom Theater View skin that would follow your store's graphical identity. I think some skinners here would be happy do that kind of work for you.
Personally, I would check the local copyright laws before proceeding. Copying commercial Audio CDs to a hard drive and allowing customers to play the files may not be automatically permitted even though the purpose is only to demonstrate the products. It would be best to get written permissions from the CD distributors, record companies or other copyright holders.
Perhaps JRiver could extend the Party Mode password lock to Theater View too. Then once Theater View is started it would not allow exit to Standard View unless the user provides the password. This would be a useful feature for real parties too. The guests would not be able to accidentally close the Theater View.
