iTunes 1 and 2 worked with OS 9, though they don't have as many features as the newer versions. You can get iTunes 2.0.4 (which I believe is the latest release that'll run on OS 9) from here:
http://www.versiontracker.com/dyn/moreinfo/macos/9688
If you're running 8.6, you can hack iTunes 1 to work with it if you really want. The patch is available from here:
http://www.macupdate.com/info.php/id/5401
For other options, SoundJam MP is basically iTunes before Apple got their hands on it. You might find it hard to track down a serial number for it though since it was Shareware and is no longer sold.
Panic's Audion is now available for free, and probably has the most features for OS 9, so I'd recommend that:
http://www.panic.com/audion/
I'm not sure if any of them are compatible with the remote though.
Finally, you could install Linux on the Mac and run a player on that. There are quite a few available:
http://www.google.com/search?q=linux%20music%20player
http://www.versiontracker.com/dyn/moreinfo/macos/9688
If you're running 8.6, you can hack iTunes 1 to work with it if you really want. The patch is available from here:
http://www.macupdate.com/info.php/id/5401
For other options, SoundJam MP is basically iTunes before Apple got their hands on it. You might find it hard to track down a serial number for it though since it was Shareware and is no longer sold.
Panic's Audion is now available for free, and probably has the most features for OS 9, so I'd recommend that:
http://www.panic.com/audion/
I'm not sure if any of them are compatible with the remote though.
Finally, you could install Linux on the Mac and run a player on that. There are quite a few available:
http://www.google.com/search?q=linux%20music%20player