Anyone ever watch Stargate SG-1?
No? Well there was an alien race in that show known as the Ancients. They were by far the most technologically advanced race in the entire universe. They eventually gained ultimate enlightenment and became a race of gods, more or less. Before that happened though, they created what has since been called the "Replicators" (Or perhaps the Asguard made them, I can't remember. The Asguard are basically your typical Area 51 aliens. ) . Originally intended, if I remember correctly, as civil servents more or less, they quickly developed rational and independent thought. They're a robotic race made entirely of nanites that combine into a tangible functional form to best cope with any given situation (usually bug-like spiders.) Eventually they're capable of forming into human analogues that are indistinguishable from a normal human. Even exploding, shooting, blasting or otherwise destroying them has no effect: They simply reform shortly afterward.
They can assimilate any technology, even Ancient technology, to further their own abilities. They can't be beat because any weapon, no matter how advanced, simply makes them stronger. Hull, ship designs, jump capabilities, phasing, they'd have it all and more. They improve upon anything they acquire, making it better in some way.
Get where I'm coming from?
Nanite creators? Check.
Advanced technology? Check.
Can't do a thing to stop them, even though the Vasari fleets are hinted as being huge? Check.
Their vast use of nanites, their fundamental technological might, and their powerful warships, all defeated so badly that entire sectors were simply "went dark"? If what's after the Vasari are not replicator-esque, I will be suprised.