I've been having a discussion in the lab about my recent amp switch project (
http://www.audiocircle.com/index.php?topic=49984.0) and it occurred to me that a similar speaker switch might be a good project for your class. It wouldn't need the dummy loads and you could simplify other parts for cost if you wanted. It would allow the students to better hear how different speakers sounded different, particularly when paired with your new measurement system so they could hear how measurement and observations corresponded.
Naturally you could buy one or someone could send one to you, but I wondered if it would be a project of interest by itself. I think relays are neat physics examples because they combine electromagnets, springs and electrical switches.
