Out of the ones listed definitely the Audio Power Pack II. It does the best job in my opinion and has a detachable power cord, so you can tweek that system further with a better cord. They do give you a good fat one with the unit new.
The Monster is OK and will do a decent job. It is well like by many for the cost.
I would avoid the Adcom. A few I heard actually added noise to the system.
Another nice unit in that price range is the Vansevers Super Companion.