I notice the gamma in Epson scan is set at 1.8. CS4 is probably displaying the images at 2.2. That would definitely cause a colour appearance shift on your display when migrating an image from the former to the latter. As for why your prints are coming out too dark, you probably have your monitor too bright. Have a look at Andrew Rodney's article on this website "Why are my prints too dark" gere:
http://www.luminous-landscape.com/tutorials/why_are_my_prints_too_dark.shtml