sennheiser momentum on ear. i own a pair of these and i say the sound is warm, good bass and mid. high is clear too. generally it is a quite balanced headphones with mid and bass slightly forward-ish. but the clamping force is... i could only wear those for an hour max before i have to let my ear to rest for a while. but i guess it's normal for on ear headphones unless you get a pair of bose oe2 (beware of fakes in plaza lowyat though).
i think sound leaking is not an issue anymore because almost everyone in the lrt has headphones/earphones on (thanks to iphone now everyone is listening to music, but with apple's cheap earphones and they leak, A LOT! )
i am using a pair of akg q701 and i say it is perfect for everything. i am on Asus G53sw so i dont have a pcie sound card but im using asus xonar u3 usb sound card though. so i just tune the eq to treble when playing cs:go for sound whoring and default when doing everything else.

comfort-wise, it is comfortable for me but yeah, the headband is a little bit of getting used to but i am used to it now.

sorry it is a opened-back headphones, but sound quality is top-notch.

for amp, my setup = xonar u3 -> fiio e12 on +16db gain -> akg q701, no problem whatsoever.

All-rounder + Mic + Budget RM400 IEM:

[+] Audio-Technica ATH-CKM500iS
[+] Audio-Technica ATH-CKS55XiS

* Mic only works for phones not for laptop
Open + On-ear / Over-ear + Budget RM900 headphones:

[+] Audio-Technica ATH-EP700
[+] Audio-Technica ATH-AD900X
[+] AKG K540
[+] Sennheiser HD239
Comfort + Closed + Budget RM1XXX headphones:

[+] Audio-Technica ATH-A900X
[+] JVC HA-SZ2000
[+] Sennheiser Momentum
[+] Sony MDR-1R

Why not HD600?
Have you compared this with Hippo Pro One? I want to get SE215 but well, the connecter issue is holding me.