Hello Colin. I too have tried various things suggested here to try fix this problem. None have worked.
Today I read the TidBits newsletter and they noted various problems with 10.6.8 such as ours, and also audio ones and another with the dock (which I experienced as well).
I fixed the dock problem by downloading an update to Parallels.
The folk at TidBits suggested that sometimes an effecitve solution to misbehaving updates is to download the 10.6.8 combo update.
I tried that, but I am sad to report it has not fixed our printing problem with the Epson RX650.
On a more positive note, I can tell you that an interim step you can take is to use the Gutenprint Driver. You do that by adding another printer, selecting the Stylus RX650 again, but selecting the Gutenprint drivers.
The list is very long and the RX650 is not specifically listed there, but I have been able to do basic text printing. I will experiment to see whether I get better results with other model numbers. I have not yet checked whether these driver will support the disc printing facility. I used to use that a lot and had printed hundreds of CDs. Luckily my clients no longer need files supplied on a CD and can get them online.
I do hope we get this mess-up fixed. The 650 is a great printer and I don't fancy having to replace it just becauase the driver and other OS components have been screwed.
Good luck.