It will be better if you enter, rather than record, your songs because the resulting MIDI files will be more precise and will include the bar lines. It isn't much harder to enter a song in MuseScore than to record it. It might even be easier depending on your playing ability.
As a bonus, starting in Synthesia 11, you can generate XML files from your MuseScore file and have a high quality sheet music display. You should also be able to produce XML from a song you play into MuseScore but I have no idea of how good a job MuseScore will do on producing a correctly notated piece of sheet music from something you play.