Genio translator, to be checked in Application Add-ins, can import MX text files (Genio) to ALG and DTM.
You have to set a translation table (.ggr file) from MX strings to alignment or features.
MX has several string types that are related to dimensions (number of information stored at each point of the string).
I would say that only MX geometry strings (12D G??? strings) should be imported to Rail Track Alignments when both G and M are available in MX.
When you've got only the M string (6D) it can be also translated as alignment but the definition of geometry is not complete. Check the result.
If something goes wrong with the import, try to exit rail track and come back again to load ggr and file to import with no action on the groups.
If something still fails try to uncheck some groups to see which one can cause the issue.