Weighing in:
I would NOT use a graphic EQ unless its all digital and specifically does NOT emulate an analog graphic. The reason being that analog graphics introduce lots of phase shift for every slider that is not set to -0(it might be possible for a plugin to be done with linear phase, but I am not aware of one).
Fabfilter in its linear phase mode should be a good choice(do remember to bypass it whenever you bounce out a mix).
For any EQ to work well in this application, you need some way to do accurate measurement. SMAART Live or Spectrafoo, along with a decent measurement mic would do the job pretty well(user experience/skill making a big difference).
The lowly EQ III 7 band can do a decent job(the measurement process probably makes more difference than the brand of parametric EQ).
Speaking from my own experience, system tuning CAN make a serious improvement if done right(of course, badly done and all bets are off
). My first commercial room was small(at 12'x14') and even with lots of trapping and wall panels(all Owens Corning 703), I had a huge null at the mix chair at 50Hz(on the couch behind me was close to perfect). Adding a sub made a very modest improvement, but adding a digital EQ on the way to the sub, and tuning it with SMAART Live, I was able to get the mix position nearly perfect. Keep in mind that this tuning is going to help in 1 spot in the room, and NOT the entire room. If I had a producer on the couch, the sub stayed off so he got the "good" seat
