If it is a 4200 onboard, you can not pair with a 4300. Generally it can pair if the first two numbers of the model are the same. For example the 4870 can pair with a 4890, but not a 4770. It is more likely it is talking about hybrid crossfire, where if you were using a powerful card it could offload small tasks to the 4200 when not doing anything GPU intensive to save power. Not sure about that though.