There's an interesting book called The Race for a New Game Machine: Creating the Chips Inside the XBox 360 and the Playstation 3 by David Shippy and Mickie Phip

There's an interesting book called The Race for a New Game Machine: Creating the Chips Inside the XBox 360 and the Playstation 3 by David Shippy and Mickie Phipps on the development of the Cell processor. I can't recall if if had all the details regarding adding a GPU to the PS3, but I remember it had stories about the awkwardness of having the IBM Cell team also working on Microsoft's Xenon CPU for the 360, which IIRC used modified Cell PPE cores.