I use Foobar2000, it has 2 built in EQ's , under the View Tab, click Equalizer(18 band) or Graphic Equalizer (32 band), then adjust. iTunes is basicly the same under the view tab, its even more basic than Foobar. It's been a while since I added anything to my Foobar, the 32 band version is an add-on I believe ( http://www.foobar2000.org/components/view/foo_dsp_xgeq ) unzip it and drop it in the components folder of foobar (mine was ... Local Disk (C) - program Files (x86) - Foobars2000 - components ) , then restart foobar.
I've played around with other players that have more advanced editing setups like Goldwave, has some pretty cool stuff, its a demo to buy program, like a lot of them. But for just tweaking your headphone setup, this should work just fine. A parametric EQ is a little more advanced, it allows you to do custom EQ's where you chose the frequency and the shape of the curve, this allows for cutting or adding boost in a very narrow way, to correct a problem. Ill try and see whats available and play with one before I go so far as to recommend one. Here's a link on a "how to" that might help http://audio.tutsplus.com/tutorials/production/how-to-use-a-parametric-equalizer/ .This tutorial is for Pro tools LE, found a version for $69, so there are options you might have to purchase.
But the EQ's in Foobar would probably do just fine. I use Itunes mostly to manage my music on my iPod and for ripping, and do all my playing on foobar. I know there are a lot of options player wise, and most have an EQ build in. I don't mind doing some addition research on the subject if needed, I just don't find the need to EQ my headphone setup, but a lot of head-fiers can't live without them, perhaps one of the resident engineers with expertise in this area has a favorite one to recommend. Hope this helps some.