The Magnar sovereign is male.
the Trog is protecting herself with the Sword. The Magical one has a very deadly and intimidating pose, as well as her legs actualy not being as spread as the others. The Magnar is thin because he is an elf. His Chest plate is exactly that, not a breastplate. Also the expressed image of the face is quite masculine and the hips are not wide enough.
The Magnar guy, in form of body, looks much like Krax, while the Trog and the Uxen have a very similar pose as well.
a Female dark-elf would mostlikely wish to look both imposing and alluring, as opposed to Trog and Uxen whom merely wish to look imposing and scary. Part of that imposing is using their wide hips to large visual effect, or perhaps the Artist approached the result backwards since there is no actual physiology at play. This Magnar is merely only looking imposing with a hint of lithe, and absolutely no emotion on his face. He has long and full white hair, this is true, however its not being used in any sort of ornamental fashion. He is pure warrior, even if he doesn't have the Mass you would expect of a giant warlord, however if you look at the rest of the photos the Men are either Rogue or Sorceror while the females are in more of a warlord stance. I would imagine a picture of a Magnar Female Soveriegn to be even more imposing ... and above all to look 10 times as deadly while at the same time to have a Dominating, yet very female, allure. To assume the Magnar is male is, to me, a lack of imagination as to what a demon-elf female would look like. If nothing else, look to the hips, as well as the similarity of stance that the Krax and the Magnar Sov's are standing.
I would assume this Magnar fellow is more or less a stand-in, a Regent for a more powerful Female Elven Sorceress or Warrior. I could be very mistaken in the relative powers of this Male Magnar, although I have a feeling he is "Mediocre" when it comes to Magnar generals/channelers. In any case, powerful as he may be (to my lack of knowledge) I am very certain that he is male.