One thing that might be a factor...
I used to think that my Epson 2200 printed significantly darker than the screen, too, until I happened to carry a print under a really good light. I had been viewing the images under a skylight or in a room with a halogen lamp before. Directly under a bank of fluorescent tubes, however, the print looked pretty much just like the monitor. It became obvious to me that how well a print's brightness matches the monitor depends on what sort of light you're viewing the print under. Is it possible that you are viewing the prints under dimmer lighting conditions than the printer drivers are optimized for??? You might give it a try under a brighter light (maybe something like gallery-style lighting, if you have access to some) and see what you think.
Lisa