I don't have X1 or X2, but I assume/IIRC you don't export TO anything, but you choose the tracks as the export source, which leads to individual per track wav-files. I'm a bit tired now, though, so I may be distracted :o/ I expect export in X-versions to be similar to that of 8.5.
You can't export TO busses, as busses are inside the project and your intention is to get the material OUT of the project.
(Oh. I see you edited the wording.)