I've been trying to figure out how to do this on a mac for ages, do you have a tutorial anywhere?
Ill find it in a sec... but looking I found this as well, but is $20 but may work easier
http://www.prosofteng.com/products/hear.php
I cant find the exact instructions right now but it is pretty easy...
you need AU LAB (bundled with Xcode and you need a free DEV AppleID)
Soundflower
And 2 separate copies of LineIn (just duplicate a downloaded copy)
After soundflower is installed, go to System Preferences > Sound > Output and set it to Soundflower (2ch)
Then open 1 copy of line in and select the input at Soundflower (2ch) and the Output at Soundflower (16ch). Hit advanced and make sure the channels are 1-2, 1-2
Open AU Lab (Developer > Applications > Audio), and hit next, and on the next window hit add input, then next. Set it to Soundflower (16ch), and MAKE SURE the outputs are on channels 3-4 (just drag the slider)
It will then give you a window, and on output 1, you can set it to graphic EQ.
Open the other copy of LineIn, set the input to Soundflower (16ch) output to system output/headphones/speakers (you might have to fiddle around there). Hit advanced and make sure the channels are 3-4, 1-2.
All sound is then EQd.
It takes a bit of work but its great
