iWatch is said to debut in Fall.  Now with iWatch, full of biosensors, it will be impossible to connect to headhones. So expect Apple bluetooth headphones, designed exclusively for sport activities and maybe jogging. Might be also good for calls and must have remote. With all this, you can't...

Man, you already have hundreds of apps for iOS with equalizer and built in equalizer in OS7 works too. Not sure what you asking for, its already there.

Now, while Apple's own earbuds not bad at all (some say even one of best in their price category), there is a lot of room for improvement. Apple surely would need some help in this field, and best probably would be to OEM Beats IEMs, but with better, not bass-heavy sound. Beats Tour IEM with...

There is built in equalizer with profiles in the settings app in iOS. Also you can use free apps that allow you to customize your settings even according to your headphone (they have a database of headphones and best profiles for them). I use Groove which is great for me, but you can use Beat...

A USB sound card will do, like mine Creative Omni Surround 5.1, does have RCA outputs

Sony AS30G, using for about 8 years, for travel and workout. Very good sound

Yeah, I bought on my trip to Japan Beyerdynamics dtx501p and a pair of JVC HA-S500 as gifts at about 39 dollars each, thats I believe was good deal. 

My favourite Seiko

Well, it was just my hypothesis. I think that we can see how the expensive phones frequencies look and just compare to mid to low price phones, especially of DJ and bass head style. In that case, probably expensive phones will have more natural, balanced sound with better higher frequences...

appleTV

Beyerdynamics dtx501p

HD558?

I think it has something to do with age. As we age, hearing loses higher frequencies. Therefore, high end models are bought by wealthy people who likely have to lost already some part of HF hearing and therefore, brighter phones for them will be sounding better.   As for cheap phones for...

on iOS, there are two great apps for music listening. Groove and Audissey, the former has best interface of any iPhone app and the latter one has settings for various headphones. 

itunes 

I have same HD 449 as you and with USB sound card Creative Omni 5.1 with 600 Ohm headphone out it gives excellent bass. I didn't try HD from onboard audio but my impression that it might be less powerful and therefore, less bassy. 

Bose Companion 20 is a great speakers with wonderful bass and sound quality.

Sennheiser HD202II. Clamping force caused me headache. Otherwise, nice sound and price.

I have Beyerdynamics dtx501p for travel - it comes with travel bag, airplane adaptor, foldable, has wonderful bass and clarity, great sound.  For desktop I use HD449 Sennheiser and both are wonderful. 

Sennheiser HD 449 - it has great bass (very clear, not heavy, detailed). 

As HD 449 user I might be biased, but this model has great clarity, developed wonderful bass and is very comfortable.

Informative. Useful. Some benchmarks or comparisons. No bias. No judgement. 

Creative Omni 5.1 has RCA output, line output 3.5 mm, headphones 600 Ohm output.

Beyerdynamics DTX501p is my favourite

Magnets needs to loosen up - now thats funniest thing I ever heard. Bother to describe how they loosen up exactly? Do they become weaker, lose their electrons or become fatter and wider with age? :)