So - following in the vain of the above I give some info on how to control the outputs of your OSX systems. OSX, albeit the best platform for audio/visual mixing has limited control of the main audio outputs. Volume levels and that's about it. It frustrated the hell out of us Audio Engineering types as we sometimes need a Multiband EQ to fix room / speaker deficiencies or a multi band compressor for when we send it off to a home theatre system.
So if your chasing that sort of control over your OSX sound outputs just follow this piece written by a good friend and professional audio engineer of over 30 years.
Takes a bit of knowledge so if you don't understand EQ or compression best not to use it. I have seen it work correctly on every OSX from Snow Leopard to Mavericks. There can be some issues at times but just be persistent and it should work. I have also had it operating on my Hackintosh system.
OSX System EQ (compression and most other effects)