If Danny says it works..I'd roll with that.
We did something a little backwards, I put the file through the rip to test it out and it worked great. I ran the PDF from PhotoShop through the RIP, then took the TIFF files into corel and added registration marks. Just to see what would happen. The job turned out amazing. I had to recut 5 of the screens since i didn't like the colors. Didn't even need the marks...oh well.
I've been having trouble importing a DCS EPS or whatever it is into Corel recently. The files get really jacked up.
A .ps file is a postscript file usually from "print to file." We use them out of Corel for our spot color and simple halftone jobs. Simprocess is run through Photoshop. The screens of the Douthitt are killer. I mean, just stunning. We did a 4cp on darks the other day and you had to look to find the dots at 65lpi. The design wasn't flawless, but it was good enough to run. If I would have had more time from the customer I would have worked on it a bit more.