The news from RebusFarm are that they now support Corona Renderer 1.6, however the CXR format is not yet supported.
The support for CXR will be added as soon as possible, probably this or next week.
If you experience any issues with Corona Renderer 1.6 and RebusFarm services, pleas report them to us at support@corona-renderer.com, or to RebusFarm directly at info@rebusfarm.net.