I can run my floorspeakers to a decent level with my headamp.
Not as loud as my 2*150watt sourroundthing, but closer than you would expect.
They have some numbers on GDaudio´s page that says it delivers about 15 watt in 8 Ohm.
It has caused no problems at all.
So I have done and do it the other way around, my headphone gear is of much highere standard than my regular hifi so I had to try..
Lots of guys run their HE6 from speaker amps, also AKG K1000 is often driven by speaker amps.
So if you are carefull with the volume I guess it is worth a try, they will not explode as soon as you touch the knob, but they will take damage at high levels.
I once blew up my Ibuds, just for fun, it was done with a speakeramp and they survived much longer than expected..
I am not a techguy, but the danger to amps is shortcircuit, because of the Ohm in speakers goes to low, I do not think there is problems the other way around..
Give it a try and come and warn us about it, or recommend it if it works great..