How'd you manage to have both 8.2.1 and 9 installed? It should be either one or the other. iTunes installation replaces the prior version or writes new files if there is nothing to overwrite...
Do you have a second drive with either a Super Duper! or Carbon Copy Clone of your system from before you upgraded iTunes? If so, you could make a new clone so that it also has 9.0, or you can right-click one of the .mp3 files and choose Get Info. From the Open With pulldown select iTunes 9.0 and then click the Change All... button.