So, you aren't actually building this? I don't know who made the restraint of this system being under 3 pounds because that's not going to be possible. Any case you buy is going to over 3 pounds, even mini-itx/htpc's. The closest you are going to get to what you want is a ultrabook with a discrete gpu. I know there are a couple out there, but they are pricey. You're also basically describing what the "Steam Box" is going to be. Look at Intel's NUC or XI3's Piston. Those are what the Steam Boxes are going to be.