I personally find ZX2 paired perfectly with Z5. A lot better compared to my UM Mentor and SE846. Not that Z5 is clearer...but the 3d imaging and the dynamic driver bass...no contest...this 2 ba iem had being sitting in the closet for quite awhile now.
Also try PHA3, Cryin C5 and Fiio E12A. Best sounding amp is PHA3 but the bass is much weaker compared to E12A. Close fight btn C5 and E12A but in the end, got the E12A because C5 bass sounded a little loose. It had more forwarded mid then E12A but unfortunately...no contest with PHA3.
Personally...for bass...E12A and it is less then 25% of PHA3 price. For ultimately sq among the 3...PHA3...and set you back 4x the price of E12A and C5.
Do take into account....I am quite a basshead.