I'm not familiar with the MC-500. Was the system disk on a floppy? Roland UK supply a lot of system disks for older gear. Normally if they still have the software you can send them a blank floppy and they will make a copy for you free. It maybe worth a try! good luck.... If not try contacting Delatronics in the UK they may be able to help. http://www.delatronics.co.uk/news.htm