The default, I believe, is to play a looped track twice through, then fade out for 5-6 seconds after the second loop and play the next track in the file. There isn't any way to change that without rewriting the NSF codec to use a specified length of time to play a looped track rather than a number of loops to play through before fading out and moving on to the next track.
The only thing I know someone can do is set the repeat mode to "one" to continue looping an individual track over and over again until it's manually skipped to the next track. Skipping only works going forward, though, skipping back will return to the first track.