youre problem is you listen to rock , sealed sucks for rock , you need to go ported. And i talk from experience so let me tell you what ive HEARD.
i had a xxx and 2 koda 10's, i listen to lots of korn the drummer david is VERY talented(at least in there first 2 albums) he used LOTS of fast kick bass.
I have my 12 xxx ported 35hz 2.5 , very loud, very clean, the kick in my rock music is very nice and well defined(800rms). I tried my xxx sealed to see my rock music improve and honestly i lost a lot of the kick bass but the bass guitar sounded smoother.
Oh well i heard that a "small" sealed box will give you the "kick" in rock so i have 2 koda 10 laying around so i put them in a .5 sealed box!(****ing tiny) i had 2 of these and man they **** ***.
I hated my fact there was no kick bass in my rock music with these "sealed" boxes and did not expect a ported box to sound better than sealed.
oh and the rap with the xxx sealed was good and rap with koda 10s was non existing.