When I install the second disc, wait for the autorun, then install the second disc, it takes it's sweet time asks me if i agree to the licence agreement then after it installs the DLC never appears.

I had this exact problem. What you do is you go into the "Data Files" part of the menu when it first appears, not before it goes full-screen, after installing both discs and running the first disc again. You then select the box next to the DLCs.