F700
Headphoneus Supremus
I second your statement. The ZEN is source, amp, tips and even cable (to a lesser extent) responsive. It allows room for experimenting.As some of you have mentioned, the Zen does change its tonality depending on the amp more than usual.
I recommend using it on a warmer source like the Ibasso DX160 or the Schiit Asgard 3 rather than a brighter one like the JDS Atom.
(my own 3 sources)
In my case, the best combination is: max. 2mm wide aperture on the tips, secure fit and deep insertion, pure silver cable, neutral amp and warmish source. EQing might help, but it's not mandatory.