The now super advanced E.U.P. sends scouts ships to other galaxies, including this one.
Any Dyson sphere built around a neutron star would have veeeery heavy EMP shielding and redundant systems, so the Quadys is still running nominally.
After being complete, the massive neutron star emmits powerful shockwaves and EMP's, the shockwaves are able to temporarily chip off bits of the Quadys, Slowly, but surly, it gets wore down, eventually, hitting the internal systems, EMP's sweep in and disable part of the machine, that part happened to be one of the magnetic control cores - The neutron star, with less magenetic control over it keeping it from collapsing, slowly collapses, slowly but surly, collapsing.
(Also, note weak spots, If an EMP is shot at a gun and goes through the barrel, you can bet that that EMP is going to do some damage. Tacterian ships are pretty much aimbots at this and always seem to hit the weak spots)
(tacterian EMP attacks are actually quite powerful - They also have damage and explosives and such, so they can pierce anti-EMP armor quite easily)
It's hardened against EMP attacks.
The tacterians admit that they should've went there route... But they still say that "A star this unstable would be really hard to keep in check, it would easily launch huge EMP's to make the quadys go down, At wich point the magnetic feild manipulation and such would go down, than boom goes all life in the galaxy that isn't protected
Well, actually, it's just a small matter of redirecting the natural magnetc field of the neutron star. The QuaDys has several times the processing power of the Taristan Brains, even when all of the particle accelerators are running.