The iMac has a color calibration utility built in. Look in the utilities section on HD or use search function. That`s what I use and it works well.
The Epson software has an advanced tab with offsets you can make for color and density if prints do not match.
Start there and see how it goes.
To set up your offsets, make small prints, say 1" x 2" and keep moving it around on the paper and you get a whole lot of tries fast and cheap. Once your are close, put four 4x5 on an 8x10 , different photos you want printed, tweek the offsets if necessary, and make your large prints. It will work the first time.
would also tell you not to mess with color bal. Set the camera to sun, shade,indoor or whatever and keep it off automatic. I have yet to see a digcam that did not produce correct colors if used this way. Stay off automatic WB.
My last advice is to get a file with good reference colors and open it in PS along with something else that needs correcting and make a match. In experienced eyes are easily fooled and comparison is better than memory.
See if Adobe 98 is available for a Mac. That has a grey scale and reference colors. If not make a file in sun of a MacBeth Color checker chart.