From the sound of it, it seems the MAC FTP client is not sending port commands for data transfer. Or, the MAC FTP client is issuing some extended FTP commands that the PIX doesn't recommend and is dropping the request. You might want to doublecheck PIX's log or FTP server log.
You can indeed turn off fixup protocol FTP. To figure out if this is a PIX issue, disable the fixup protocol and on your access list, permit ip any any. If this works fine for the client, then it would show that the problem is on the PIX. If not, then something wrong on FTP client as it might be using non-standard FTP commands. Is there another FTP client on MAC you can try for troubleshooting purposes.
HTH
R/Yusuf