I'd say that the Augment trilogy works excellently and equally as a prequel to both Space Seed
/Wrath of Khan
and Into Darkness
. Frankly, the race thing doesn't register with me since Khan's was obviously never a Sikh (Marla's identification of him as such, before she knew who or what he was makes no sense since he was clean shaven and had a waxed chest) and has noticably white skin in Wrath of Khan
(they dropped the skin-darkening make up). Add to that his followers all turning Aryan in WoK and you have a VERY jumbled backstory indeed.
Back on topic, the ENT Augment trilogy forshadows Khan's effortlessly whupping Kingons, and the healing of the little girl. In the exchange between Archer and Arik Soong in "Borderland"...
SOONG: They're the future. They're stronger, smarter, free from sickness, with life spans twice as long as our own. You, more than anyone, should appreciate what this means.
ARCHER: Why me?
SOONG: Your father suffered from Clarke's Disease. His final years were marked with extreme pain.
ARCHER: My father has nothing to do with this.
SOONG: He didn't need to suffer. Genetic engineering could've cured him. Those who want to suppress my Augments are the same ones who condemned your father to death.