Hey guys, I know that this is an old topic, but I just figured out how to do this. You'll need two pieces of software, Audio Hijack Pro and Soundflower. It also helps to have a easy menu sound switcher called SoundSource. You click on a small icon that looks like a headphones and it allows you to quickly switch audio devices.
1. First, select your normal sound source (built-in-output or whatever you use).
2. Push the volume to the max, or near max.
3. Next, select SoundFlower (2ch) as your output.
4. Open up Soundflowerbed, which makes a small icon in the menu that looks like a flower. Click on it and make sure Soundflower (2ch) is set to OFF.
5. Open up Audio Hijack Pro. Select the Input tab, and your Input Device set it as Soundflower (2ch)
6. Click on the Effects tab.
7. Click on a spot to insert an effect, click on the menu 4FX effect, and 10-band EQ.
8. Viola! Graphic EQ that works globally across the whole Mac.
The idea: Your output is being sent to Soundflower (2ch) and you use Audio Hijack Pro as the input. It has a built in EQ, which adjusts your sound before you hear it!
Hope this helps!