Rims too thin for Schwalbe Marathon Plus tyres?

Hi all - my first post on the forum. I have a Cannondale Bad Boy (2016), whose rims are Cannondale C3 Bad Boy, double wall, 32-hole, and comes with Schwalbe Kojak Race Guard, 700x28c tyres. I have purchased Schwalbe Marathon Plus Wired Tyre with Smartguard, again 700x28c. The problem is that they simply do not go on, not even a little bit! I have read other forum entries discussing the difficulty of fitting these tyres, but my problem seems a bit more fundamental, as the rim gap seems physically insufficient for both beads and the tube valve, and indeed I have been unable to fit even both beads into the rim away from the valve. So, is it possible that this just is not compatible? Thanks!