regarding the proper selection of headphones for a walrus.... (i am joking. i could not resist.)
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the hd558 is a good all-rounder. fairly neutral, decent soundstage, decent comfort, enough but not deep bass.
good choice if you want something more easy listening and are not interested in as bright energetic treble or deep bass extension. there are other headphones which are a bit more vibrant sounding however those can get fatiguing as well.
sound leak could be an issue with any open cans however that depends on distance as well. even at moderate volume people more than a few feet away will have a hard time making out what you're jamming...