Hi Carl,
A couple additions to the discussion so far.
1. "My prints are too dark" is a very common query. I suggest starting by reading the top two Google hits, the article from Luminous Landscape and the article from Northlight Images.
There are many causes. Those articles will inform you what they are.
2. You may be able to modify a single workflow in order to have prints from one printer match the images you see on-screen. While that is useful, it is not (except by luck) applicable to any other workflow, or any other hardware. A significant danger of this is that when you change your hardware, _all_ of your images will need to be re-adjusted.
I edit tens of thousands of images a year. I want my edited pictures to look the same regardless of what hardware my clients use or what hardware I might be using next month or in two years.
That is why I recommend a color-calibrated workflow. Calibration is the process of providing a hardware-specific set of adjustment to each device. The devices are calibrated to standards. The end result is that any image you produce on your color-calibrated hardware will look the same -- and print the same -- on any color-calibrated device, anywhere, at any time (within the limits of the devices, of course).
This is fully explained in terrific little book, Abhay Sharma's "Understanding Color Management". (Not up-to-date, but not at all outdated. Also not inexpensive.)
The only acceptable color-calibration is done with photospectrometers. The built-into-OS-X color calibration tool is better than nothing, but should in no case be considered a substitution for the accuracy and reliability of a hardware calibrator.
As Léonie kindly pointed out, I have posted many times about color calibration. This post probably has the most usable information.
Feel free to ask more 🙂 .