You say you want a laid back/clinical and exciting/bassy and trebly headphone, but sometimes people mean completely different things when using these terms.
Someone i know loved my HD558 sound in the first 5 hours, i hated it cause it gave me headaches, after the mod he hated them and i loved them.
Warning: Dysfunctional redundancy ahead.
Well i have the 558's, but at first i hated them, cause the bass was way too strong and was causing headaches ( still needed to "burn in" ) , so after 50 hours of use it got better, but now the annoying thing was that because the bass become more acceptable to me, now the treble was sounding muffled, it could do a lot better.
So i Googled, and i found this easy mod, that everyone can do, turns out Sennheiser has applied some sort of foam across the middle of the cups, causing it to cover easily 40% of the tiny holes that the driver uses to suck in air.
So after the mod, the bass sounded well enough to my then untrained ears, but of course i discovered the crystallizer thingy on my sound-card, making the hd558 sound better then how they sounded with the mod alone( not neutral/laid back at all, to me that as )
But as said by PurpleAngel, if you could tell us the source (sound-card and codec used for the songs, such as mp3 aka lossy or flac/wav aka lossless audio ), that could make a world of difference.
For example, i was happy with my HD558 and ALC892 onboard + Crystallizer ( and tons of mp3 files, later became all flac files ), but after buying the Asus Xonar STX, the HD558 sounded MUCH MUCH better!!!!, i was almost regretting buying the Beyerdynamic DT 880 PRO, but that was before i could listen to the DT880's.
And it also depends on how you as an individual listens to music, are you someone looking for boosted cans, or do you prefer neutral/natural sounding headphones?
And do you happen to play a musical instrument?, if so what are you playing, i ask because a bass-player will most likely focus on the bass in songs because he/she knows that best.( assumption based upon my frame of reference. )
TL;DR
Soundcard > on-board or dedicated ( pci/pci-e )
Format > mp3 or lossless
Preference > boosted or natural/neutral
Musical instrument > what do you play or what do you prefer
Genres > which one do you like or use
Volume > at what volume do you listen mostly ( @ PC like 10 or 20 from 100 at the volume control )
What type of listener are you > actually listening to the whole song, or do you focus only on vocal or instruments , or is it only for background music or gaming etc.
Derp.