ReefMaster doesn't yet support XTF file import, but this is currently in development - so it will happen, but probably not before autumn of this year. When that work is complete, you will be able to view sidescan but for now you are restricted to depths only, because this is the only information present in the CSV files that the IMC generates.
It might be possible to replay the file in your unit and record it as an sl2 file, but I don't know if this will work. I'll look into it..
In the future it would be better to record your sonar logs as SL2 files.