Don't have any ideas other than using them to play background music during Halloween night. If you could donate them to a charity for resale, that'd be great instead of them going to a landfill.
I use my old system specificly for halloween. Painted it all spooky like and keep it on the table with the candys. Have speakers around the yard for the cemetery sounds cd.
Not really a prop but it has saved me from using good equipment and if it gets damaged or wet, big deal