While your allies take out the last of Spectrum's forces, steal the final crystal from the top of their base and render them powerless. It'll be tough, with their strongest guardians standing in your way...oh, and did I mention that the building's self-destruct sequence has been initiated? Have fun.
(finally, the Spectrum series is complete after five years...please take the time to view the other games in the series! Shouldn't take long)