Thanks for the reply. OK, I will be using for listening at home not on the move. I want to have something with neutrality for my classical music. I very much prefer laid back, better quality, detailed, than loud boomy headphones. I will be using these with my desktop computer. Thank you!(EDIT: By the way, what do you think about the Sennheiser HD 598 for classical?)
I own the HD558s, they which use the same drivers as the HD598.
Sennheiser add black rubber tape to the insides of the HD558 cups, it covers around 40% of the airholes.
I'm guessing it makes the HD558 more bassy and less like the HD598.
So removing the black rubber tape should make the HD558 sound almost as good as the HD598
You can buy a used HD558 for $96 and a new HD558 for $123.
Which would leave you with around $125 to $150 leftover for an amp (or DAC/amp)
The HD558 has a slightly veiled sound, which I think makes it easy on the ears and allows you to listen for longer periods of time.
The HD558 headphones are the oldest headphones I have that I still like to use.
This $18 to $24 cable makes it a little easier for using the HD558/HD598 with a 3.5mm plug.
http://www.ebay.com/itm/261255113290?var=560313338477&ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649
A really cheap way to drive the HD558s is a Asus Xonar DG or DGX sound card ($20-$40).
This month Newegg and Amazon have a $10 mail in rebate on the DG/DGX.