It can work only with files directly. For -r option you may call it from "find" (option -exec).

I'm sorry, but that answer is simply greek to me...

Can you be a little more explicit on how to get the tool to work on the standard iTunes folder structure (Artist->Album->Song(s))?

Thanks!
John

I cannot teach you how to write shell scripts, sorry :)

But in a simplest case - just go to an Album directory in Terminal, this is where all those tracks are, and run the above command. This will adjust every song individually with different gains. If you want to preserve relative volume of tracks use option -a instead of -r - this will treat album as one huge track and apply same gain to all tracks.

I'd strongly suggest you to backup your collection and play with aacgain a little - you'll get it in the process a lot faster, this is rather simple actually.
And probably hydrogenaudio forums are better place to ask your questions in future.

thanks atverd,

I really appreciate all the time you're spending here on the comments!

Later,
John