ohenry, I'm far away from the iMac we use at the moment, so cannot check to see if I'm right in this, but I believe the file format is OMD, a universal file format for audio.
As for the question of Markers.... I haven't a clue, as that's not something I've had to do yet. I do know that during recording, SparkME seems to detect quiet spots and break up the recording into segments (audio detect?). In any case, you can cut/copy segments as standalone tracks, and create a playlist. That playlist is used when you click the "burn to CD" button, which launches Toast or whatever is the default CD burning utility on your system.
M.