Sorry man but I don't think you can get deeper sub bass with these headphones.
I've seen graphs for the japanese version of 7520 (z1000) and bass starts to fall off cliff at 70hz.
Knowing that 7520 is a serious monitor headphone... i think it belongs in the same class as other serious closed-headphone monitors such as akg k271 and shure srh441.
clean sub bass but sure won't go that deep.
i know this is full size only headphone sub-forum... but if you want clean/tight/deep sub-bass and clean mids to satisfy your genres (noted above) but want to stay in Sony professional brand... get the IEM version in the Sony 75XX series family.
holy moly thats a quick roll off... others were saying the bass is deep. That is worse than the hd650 bass roll off... wow.... If its true that they are the same headphone then yeah that is a no go.