No, you're still not quite getting it :p Your muscles are also helping you accomplish things, they give you a "bonus" to getting things done, but you never go "I roll a dice to see how well I use my muscles.", so the Sprite can't go "Alright, I'll help you use them muscles!" Instead you go "I punch this guy in the face." and your muscles help you do that. Seriously, it helps if you imagine the Sprite being on your computer. Would it help you there? Yes, since every test you make is trying to use your PC, directly. Now move it to your Cerebral Boosters while you're still using the PC. Will it help now? No, because the device you're using is the PC, not your cerebral boosters. They're just there to help.
Or, better yet, think of it like this: The Reaction Enhancers are a person using teamwork. So is the Sprite.
You try to use a gun that the Sprite is on, so the Sprite tries to help you use the gun: Reaction Enhancer and Sprite both roll teamwork to help your shooty action, targeting you as the leader. Alright, cool, that works.
Now put the sprite on the Reaction Enhancer: The sprite is now using teamwork on... the reaction enhancer, not you (since you're not actively using it), while the Reaction Enhancer is still rolling teamwork on you. So the Sprite would aid the Enhancer, which would aid you. The bonus would be smaller, but presumably it'd work... except that in reality, the RE isn't rolling anything, so there's no dicepool the sprite can help with, so its aid never reaches you. (also, I think teamwork on someone, so they can use teamwork on someone else better, is not allowed by RAW)