[Jmurphly]

In comparison to other headphones, I would not rate the HD518/HD558/HD598 as fragile.
As long as your not overly abusing with the them, can't see them breaking or falling apart.
I would say the my HD558 are built as well as possible, for their weight.

I say by some used HD558 and remove the black rubber tape from inside the cups, as the tape covers about 40% of the air holes.
I would assume Sennheiser added the tape to make the HD558 sound less like the more open HD598.

Here is an aftermarket cable I got for my HD558.
Comes with a 3.5mm plug and can be ordered in one of five lengths.
I doubt it changes the audio quality.
http://www.ebay.com/itm/261255113290?_trksid=p2060353.m1438.l2649&var=560313338477&ssPageName=STRK%3AMEBIDX%3AIT

Well I think the HD558s are the way to go. Thanks for all the help!

 

[Ventace]

Thank you! And yes, I did read the whole post. ;P

Anyway, do you have an experience with the HD518s from Senn? I've heard many people say they sound almost identical to the HD 558s just with a touch more bass. I can currently get the HD 518s for $50 on Amazon, so if what they say is true, I'd much rather save the extra cash.

Well yes I do, and I'd say they'll serve you well.
Compared the HD 558, it's a touch less refined, tiny bit less detailed, and it may feel a little more plastic.
It does have a bit more bass and lower mids, though I personally would still get the 558, the 518 is still fairly good.

 

[god-bluff]

You could still get a pair of Griffins. They cost nothing but are wood backed closed(but open sounding)headphones with high quality 50mm drivers that bare comparison with closed headphones like the Beyer DT150 and Focal Spirit Classic in my limited experience. Those two are headphones more on the level of HD6** rather than HD5***. Maybe 85-90% of the sound for 1/4 to 1/12 of the price. I'd urge anyone to try them and you can sell your amp! You won't be needing that