I have the same message for maximum=(2048,2048), one monitor 1440x900, the other one 1336x768, the solution I've found is to put on on top of the other, so it will be 1440x1668, or, use Ubuntu 2D and in that desktop I've saw no resolution limitations...
You can also try jupiter to enable both monitors... I've tried it without luck, but I think there are tricks that need to be done with jupiter like enable both monitores BEFORE plugg the second one in!
Sory for my bad english and good luck with that!
If you find a better solution post it here so I can try it too!