What EQ settings did you have it on?
Also - Impedance and sensitivity on this scale is far different to car audio, you very rarely ever come across over powering.
Not to mention, you'll never need external capacitors, or worry about voltage drops/spikes.. Thankfully, we are lucky in this regard !
But, be aware, you have a host of new problems. For example: Output impedance. It might not matter now, but if you ever look into IEMs, it will.
When I was really into car audio, the idea of a multi-driver IEM really interested me, and is what kick-started my interest in headphones and portable gear.
In terms of maximum handling capacity ratings on headphones, the reason those values aren't listed, is because it just plainly isn't necessary. We needn't worry about such things, luckily.
If this answer seems a bit weird, sorry, I haven't slept in a long time - long long gig hours, can't leave site, so I'm on head-fi during my breaks.