I reckon the entire Supernode theory is a load of Horse Hockey!
I think the Sathanas fleet caused the Supernova, then made an intrasystem jump to subspace and waited there till the star had finished exploding - sort of like diving underwater to avoid tidalwaves.
I agree with the idea that the GTVA must have somehow butt f****d the shivans somehow...Destroyed ultra-vital cargo transports/Blown up the first Sathanas/pulled another away from it's post/Erased the E-Pegasai Node...whatever...one/some/all and/or other stuff caused the fleet to have to over compensate for the losses and something had to give...therefore some Sathanas got shut down.
My theory about the shivans is that they are testing us. \/
They are locked in an eternal struggle with an unseen enemy in another galaxy. Neither side is able to gain an advantage the war is deadlocked and has lasted several million years. In looking for a solution, Shivan stratagists hit upon a highly unorthodox idea - any race capable of defeating the Shivans would by definition be able to defeat their enemy. The only problem - such a race doesn't exist. The solution - go Darwinian the younger races on a Galactic scale until such a race emerges.
Basically the shivans are using Darwin's theory of Natural Selection on a Genocidal Scale. The unfit races are wiped out. Eventually a race will emerge capable of defeating them. The Shivans play a long game. The plan reads something like this:
Stage 1 - The shivans observe a race once it becomes subspace capable (Explains why Shivans didn't show up as soon as we discovered subspace)
Stage 2 - After an intermediate amount of time, the shivans launch an FS1 style offensive - a genocide wave. they devestate the fleets, then destroy the Homeworld(s), after which they goe back and take care of the survivors
Stage 3 - If the race Defeats Fleet from Stage 1 they then spend some more time watching during the subject race's rebuilding process
Stage 4 - Eventually, they attack Subject race again and see how the race fares against better warships. (The whole Rakshassa/Ravana business at the beginning of FS2) - This stage is a definate pass for the subject race
Stage 5 - When the Subject race beats Stage 4, The Shivans Send in a Radically stronger vessel (The Sathanas) and launch an attack in the style of Stage 2.
Stage 6 - If the Race survives stage 5, thay then launch what appears to be an all-out offensive with a fleet of Sathanas, but they then do something with real "WTF?!" value to see how the race reacts.
Stage 7-? cycles of rebuild then invade occur untill a race capable of defeating the shivans no-matter what stratagies or stunts they pull develops.
So basically what im saying is Capella was a giant reaction test.
My my reckoning, the Ancients didnt get past stage 2 and the GTVA may be the first in our area of the galaxy to get past to stage 6 - which i reckon we passed
My basis for all this is 2 things
one) the

quote that the shivans were only part of the bigger picture
Two) Every time we fight the shivans, our tech gains vast improvements
FS1 - Thanks to the Shivans we gain
1)Shields and anti-shield weaponary
2)Enhanced normal space tracking abilities
3)The ability to track ships into subspace (Via the Ancients)
4)Fighter size intersystem subspace drives
5)Beam Weapons(developed between games)
FS2 - We gain
1) Subspace Portal Tech (Again via the Ancients)
2) Shivan Comms Tech (ETAK)
3) Beginnings of Shivan Style Weapons (Kayser)
Not to mention the Hades or Sekmet which were shivan based, or the captured Dragons/Maras and others