Aklis
Evil frickin' Sith Lord
The 'True Sith Empire' and the Ancient Sith aren't be the same.
'Under the leadership of the Dark Lord of the Sith Naga Sadow, the Empire invaded Republic space during the Great Hyperspace War, but it was defeated. The Sith Empire was believed to have been destroyed by Republic forces during the Second Battle of Korriban, but in fact survived due to a single Sith Lord who escaped to the Unknown Regions. There, this new Sith Emperor, whose rule lasted for well over a thousand years, rebuilt the Sith Empire and struck back against the Republic in the Great Galactic War in 3,681 BBY.'
This text - taken from Wookieepedia - claims that the Sith Emperor was a Sith Lord under Naga Sadow, and therefore most likely not a member of some unknown race, which, for me, would be the Ancient Sith, the species that Adas was a member of.
We also know that Naga Sadow was half-human, half 'Sith', as in the species, and as the Sith fled to Ziost - Naga Sadow's homeworld, he is obviously one of the Ancient Sith.
The Massassi are listed as a subspecies of the Ancient Sith, by Wookieepedia, and Freedon Nadd has said that they were descendants of the Ancient Sith, so, they may have 'evolved', or devolved from said race, just as we humans evolved from monkeys.
As to continue on the argument that True Sith and Ancient Sith aren't the same, yet another quote from Wookiee.
'Around the year 6,900 BBY, exiled fallen Jedi—fleeing from the Battle of Corbos, which concluded the Hundred-Year Darkness—landed on Korriban, a desolate world inhabited by the relatively primitive but unusually Force-sensitive Sith people. Using their training in the Force, the fallen Jedi amazed the Sith, and elevated themselves to god-like status on Korriban, becoming the rulers of the Sith people. As years passed, and interbreeding occurred between the Fallen Jedi and the Sith, the term "Sith" came to mean not only the original inhabitants of Korriban, but also their fallen Jedi masters. Thus was the Sith Empire born, with nearby Ziost becoming the capital, while Korriban became a sacred mausoleum-world.'
So, the True Sith Empire was nothing more than a mix between the Ancient Sith and fallen Jedi. The awesome Sith-dude in the TOR-trailer could be a half-breed.
I might even write an essay about my theories on this. But, not today.