This is pretty much what I've been saying now for a very long time. It really doesn't matter what system you want to play, or even what system you want to call it, the problem is the compatibility of the superstars in the side! You simply can't fit them all in!
Aguero is an odd one, he's quick, he's a decent finisher yet since his very first game against Swansea 4 seasons ago, I don't remember him picking up the ball and driving at a defence often enough, and having many shots outside the area. He is to a large extent a slave to the way we play, and is expected to live of half chances in crowded penalty areas where he has to kick the ball through a jungle of legs or use his pace to nip in ahead of a defender. It's a criminal waste of talent.
Silva on the other hand, I don't really want to pick up on him for the incident mentioned on here and by neville about him spitting his dummy out and sitting on his arse, and if we've picked up on it, I would expect the manager to have done so also. But regardless where you play him across the midfield, he is always going to unbalance the team. In the middle, and he needs a caretaker behind him. On the left or the right, and he doesn't provide the cover we need for our attacking fullbacks. The only position Silva can realistically play in our team, is playing off the main striker. Does he shoot enough for that job, well perhaps not, but he did ok in December, so proved he can do it. It's again criminal that neither Mancini nor Pellegrini have recognised this is where he most likely should be playing.
With those two sorted, then Toure becomes a little less of an issue with the likes of Fernandinho being more inclined to sit deep, with Milner and Navas able to put a shift in on the flanks and protect the fullbacks.
That leaves Nasri as the odd man out to a large extent, although he is perfectly able to be rotated between Toure's role and Silva's, playing him in the central role he wants, and excelled in at Arsenal.
But it all revolves around moving Silva out of that midfield, pushing him up the pitch and getting the ball to him early and let him load the bullets for Aguero with clever passes in behind the defenders and use Aguero for what his talents are made for.