I have been comparing the HiFiMAN EF-6 amp, which they developed for their HE-6 headphones, to my newly purchased Schiit Mjolnir, each driving the HE1000 v.1 headphone in balanced configuration, using the stock balanced cable that HiFIMAN includes with the HE1000. The DAC has been the Schiit Gungir Multibit, and this is run either from Lightening Connector digital output via CCA USB converter, or from the FiiO X5ii via coax.
The EF-6 has more transparency, better layering of separate instruments, and clearer background instrumentals than the Schiit Mjolnir, although the difference is small enough that if I were not listening to the two amps in immediate sequence, I doubt that I would be able to tell a difference.
I had the bias of hoping that the Mjolnir would sound at least as good as the EF-6 or better, so that I could sell the EF-6 and free up some space on my listening setup. Now I am stuck with either keeping both or letting the Mjolnir go. Darn!