I wouldn't get open cans for subsonic performance. The 770 uses the same driver (different impedance in some cases, 80 ohm suggested) as the 990 but offers more sub bass.
List from what i've heard for sub bass kings.
XB700 - May be your best bet.
XB500 (mid bass is quite boxy though)
DT770/80 - treble peak as in all beyers, test first to see if you can stand it.
M100 is nice but not as much quantity as XB series.
*POSSIBLY* the XB920/X10 - Heard these...