I know this is an old thread, but I thought I would offer my solution.
Parallel adaptors don't usually have drivers on Mac OS X. I am not sure it would help you with the print center + cups anyway which appear to run the adaptors from user space (ie. they don't use kernel drivers).
Try usbtb which works with every parallel adaptor I have tried (including a PL-2305)
http://www.buymelunch.org/printing/usbtb/
it adds an additional usb backend to cups and is faster too.
--eric