The PC speakers I'm using on my cabinet have a volume control right on the front of the right speaker. I decided a simple volume control solution would be to just use that. My speaker grilles are mounted with magnets, so it's simple to pull it off, adjust the dial, and replace.
Kind of a crude approach, but honestly, it made no sense to me to have any kind of control visible on the outside of the cabinet for something that is used so rarely.