Interesting question that I have never seen before: combining two decoders into one definition file and subsequently a single roster entry.?
Could be done as these decoder do have a series of shared and not shared CV's.
A custom definition file needs to be built.? Combining Digitrax_SFX.xml with Digitrax_01x3.xml? or portions of both.
There is no JMRI tool to combine two definitions into a single Roster entry.
If this is what your question was about.
Marc