I can't decide. I've ready that the SR-71B can drive the HE-6 pretty good but what about the MK3?
The other thing I was wondering was if the either of them have a 1/4 jack for SE cans or can you only use RSA?
Sorry if this is off topic, but I would get a speaker amp or at least a desktop one for driving the HE-6. Those are some pretty demanding cans that are usually used at home anyways.