I have the exact same problem and it's been driving me nuts. I'm using drivers off the supplied Epson CD-rom. I've not been able to get the R800 to work under OSX. (I use Tiger, v.4.8) To test the printer I finally installed the included drivers (off the Epson CD) onto an OS9.2 drive, and voila the printer works fine under OS9 (booting into OS9). But under OSX the drivers have been useless, or worse.
I've tried installing them two different ways. Once witht he printer hooked up via a firewire cable, a second time with it hooked up via USB. Neither way works. First time, I could see the printer listed in the OSX Printer Setup Utility, and the Epson Utility could see and talk to the printer (eg showing me ink levels), but attempts to actually print failed with the communications error.
Another install produced less favorable results - Neither printing software, nor the Epson utility could find the printer, and furthermore hung the system badly. The after that my system became flaky (photoshop would not launch anymore) and I had to restore everything from a back up volume. What a pain.
I can't remember now if I've gotten newer drivers from Epson site, but I don't think they're the right thing either - they are for the "intel" macs, and my mac is older (dual 800MHz G4).
Any help would be greatly appreciated.
Boris