HI,
Perhaps not the same exact issue, but I have experienced a printing problem with CS4 and and my Epson 2400. Prints (soft proofed, etc) printed correctly using CS3; with CS4 the same file prints very dark. The simple solution for me is to open the file in CS4, re-save and close it, reopen it and send it to print (using the PS manages colour, etc. parameters). The resulting print is identical to the one printed earlier with CS3. New images brought from ACR into CS4 will also print dark unless I use the same save, close, re-open, print. It doesn't seem to make sense -- after all it is an identical file in an identical work space, and it is a bit of a pain to have to do so but so far that is the only solution that I have found. I listed this a while ago in this forum and a few people responded with a similar solution.
My OS is 10.4.11
Perhaps this will help solving your problem.
Jean-Michel