The new Schiit Ragnarok seems to have more power than M9. About 1W more. Is it better than M9 ? For the HE-6 mainly. One can also use the HE-6 via its speaker taps. A bonus !
I may be wrong as I am not a very technical guy, but my understanding is using speaker taps on the Rag will not give more power than the HP out for the HE 6.