[Malfunkt]

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.
 
 
Reviews http://appadvice.com/review/quickadvice-canopener

Link to the app site http://canopenerapp.com/

 

[raidenwolff]

No idea why this isn't getting more attention. I just downloaded it and can't wait to try it out.
 
Do check out GoldenEars Accudio if you haven't yet. The preset EQ's for the many headphones / earphones that the company has measured is very impressive. 
 
I know a lot of headfiers are opposed to EQing. But crossfeed is something to be happy about in an app! And EQing is good for low-fi to mid-fi products when beginner audiophiles starting off don't have the budget for those great headphones that need no tweaking at all. 

 

[denclock]

This is easily the best music player app I have downloaded. I'm not exactly sure how it processes, but it does wonders for my m50s. I use it with my iphone, fiio e6, and m50s.  It is good not using eq, and using the m50 eq.  I was shocked at the difference versus the apple music app.

 

[Hapster]

I still prefer the Denon Club App for iOS

 

[big-ears]

I'm also loving this app.  Not found better yet.  Reduce the bass / increase the treble / add some crossfeed and my new Westone W30 and iPhone 5 now sound great together.  Even my Bose MIE2i which I use in traffic sound great through this.  Best of all, you can save all the settings to profiles and it detects when you unplug/plug so there's no danger of damaging your ears when swapping between 'phones. Nice work...

 

[big-ears]

  I know a lot of headfiers are opposed to EQing. But crossfeed is something to be happy about in an app! And EQing is good for low-fi to mid-fi products when beginner audiophiles starting off don't have the budget for those great headphones that need no tweaking at all. 

 
I'd say it's down to how your source / cables / cans / tips / ears all react together, surely?  My Westone W30 are too warm for me without EQ, and I wouldn't call them budget...