Finding information on these devices is not very easy. Just from the description of them i am somewhat curious why you are trying to use 2 modems?
Are these coax to ethernet devices?
How far apart are these devices going to be? Is it under 100 meters? Is there existing physical media that you are using like coax cable or cat5 cable?
To me, it sounds like you're trying for multi-wan. In this case, both modems would typically be put into bridge mode, and you'd need a multi-wan router that can use both connections. There are guides for doing this on broadcom, and i believe it could be done on certain atheros models with onough know-how and trial and error.