iTunes is easier than both of them IMO
Maybe so, but why on earth would you give up your manhood by joining the glowing, reassuringly expensive, plastic fruit cult in its worshipping of their lord and savior, Sir Jobs?
As an aside, newer versions of Roxio work pretty darn well. Haven't used MusicMatch since it first came out all those years ago leaden with spyware.
30 seconds of research shows:
A quick google of .m4p shows it's the DRM protected version of AAC. Apple was notorious for suing anyone who made a device that played the files and wasnt an Apple owned subsidiary, so I'm guessing the Shaker 500 can't read .m4p files. Of course the next result down from .m4p in the google search was also a result for a free file converter. So get the disc of .m4p, convert it to whatever the Shaker 500 can decode and reburn as a normal data disc. I'm sure the Shaker 500 can read directories too.
Just be sure to download from a source you trust, the converter is reputable (good), and all your security is patched an' updated. A lot of hack virus jockeys play in the shadows of the net community's freeware love fest. Of course if this is surprising, then your system is probably already a zombie....