I've been searching for something that did this well. Not only has this been created in part by a sound and mastering engineer (http://www.devinkerr.com/) who knows his stuff, but the interface design is fantastic as well.
While it has some initial presets for some gear like SRH-840s, it isn't necessary to get the benefits from this app.
If you've used any high-end studio software, you'll feel right at home with this, though its easy for novices and gives you enjoyable feedback.
The EQ only has 2-poles but is very smooth. The app also has a built-in docimeter to measure sound pressure.
In the past, I've found semi-decent crossfeed applications, but they were packaged as part of an overall 'enhancement', one that degraded the audio quality. In CanOpener, you can fine tune the crossfeed to your liking.
Edited by Malfunkt - 9/12/13 at 4:04pm