Use audio "Seek" action, and specify the loop point position in the song; I also recommend to add a small silence at the end of your song, "Seek" doesn't work if the sound ended as the tag doesn't exist anymore, then compare the current progress of the song to trigger the "Seek" action
As it is not as flexible that the two files method, it avoid the problem of a small silence when the intro stops and the loop starts for a seamless result, and you can automate it by indicating the end and loop point of you song in a variable and retrieve these numbers when needed