You'll notice the line:
FOR i = 0 TO AgmenARRAY(57) - 1
The 57th element in the array holds the number of frames in the sequence (1-16) so if you increase the number of frames in Animax!, the code will still work.
One of the reasons the PLAY statement works in the loop is that it's so short. If it were longer you'd hear the music screwing up. One way around it would be to use PLAY "MF..." (music foreground) as opposed to "MB..." (music background), which means nothing else can happen until the music finishes playing. The problem there is that your loop would stop until the music had finished.
Anyway, as long as it works.