So... running more tests on the Zero. Just did a SineGen frequency sweep and I can vouch for the absolutely ridiculous frequency response on the Zero. Chucked it on starting at 15Hz as I usually do and you can actually feel the drivers fluttering away, as you build up the presence is always there. The bass goes ridiculously low, and it is extremely stable too as I flicked the high gain switch on the NFB15.32 and cranked up the volume to see where the bass starts to distort. I got it up at around 2-3 o'clock on high gain with an amp that puts out 3.5W into 25 Ohms (10V RMS), however I'm not sure what the output impedance is for these drivers, or their sensitivity, but GOD DAMN they can take a lot of juice. I think the guys at Shozy have been playing with some black magic at their labs.
PS. I've got a little over 100 hours burnt into them so far. I wouldn't suggest anyone shocking the drivers like that without caution.