It's too bad EQu or Equalizer won't work for you. But to answer your first question, you can EQ by ear until you like the result. Depending on the goals, that could be different for each person. I try to correct different headphones' responses so that acoustic recordings sound like what I hear from live performances. For anything below 1 kHz, I find that the graphs at Headroom are a good starting point. Anything above that has much more of a dependency on the shape of your ears and your ear canals. But with patience, you can fix that too.
If you want to be more objective, follow this tutorial: http://www.head-fi.org/wiki/tutorial-on-how-to-equalize-headphones . It works very well with some 'phones. I got better results with the previously-unlistenable ER4S that I did by calibrating by ear.
Comparing the two apps, Equalizer has the advantage if you want to EQ each ear differently. Also, when you're tweaking EQu, the numbers being displayed are off by a factor of 2. It says you're cutting or boosting by 3 dB but it's really 6 dB if you measure the electrical response. At least, that's true with an iPad as of version 1.1.3. I posted a note for the developer on another thread. I think this will be easy to fix. I hope he also fixes another problem: EQu 1.1.2/1.1.3 plays stuff that's not in the original music. When I play a pure tone, the output isn't a pure tone, but one with side bands +/- 85 Hz, ~50 dB below the main tone. The iPod app and Equalizer play this tone without these artifacts. It's hardly audible with most recordings and people here have no problem enjoying their music on EQu (myself included). Maybe I shouldn't have reported this (because people are going to start reporting phantom tones that they're not really hearing). Ah, audiophiles.
