I can't think of a good concept to unify all the elements of the book, so will detail the elements here and leave the designing to the professionals.
Elements that should be on the cover:
1) The cover should have a spaceship, or spaceships. The book has several space battles in it, so I leave it up to you if it should be a single foregrounded ship, or a space war in the background.
 This requirement has been edited after receiving designs: I would like the cover to be about spaceships in some way, but no longer necessarily require a literal spaceship there. If you can evoke the feeling or idea of spaceships, that will be good too.
2) The primary technology in the book is one allowing for the mental control of spacecraft, through a "spike connector" that plugs into "cerebral slots" at the back of pilots' heads, Matrix-style. I would like this concept to be depicted somehow.
It would be great if the two concepts above are married in a striking way. [Edit] The winning design would probably be one that can tie both ideas together in a strong, unifying concept.
Optional elements that you might want to use:
1) The book features a mirroring of the two main characters. If this element were to be used, I would prefer a silhouette/abstract interpretation. But for reference, the two characters are a 30 year-old male and a 25 year-old female. The male character is a vagabond-type character with a haunted past. The female character is a space navy Lieutenant with a gift with the technology mentioned above.
2) The book uses the concept of "darkness" a lot. When pilots plug into the technology mentioned above, it is often described as "the darkness of the Whisper", a blacked-out mindspace in which they interface with the spacecraft.
3) As a personal preference, it might be nice if a purple-black starscape were worked into the background. But if this goes against your concept, please leave it out.
So like I said, these are all disparate elements that could use a good unifying cover concept.