I think this is what you want:
twistedvoid.com/c3examples/testSpeaking2.c3p
I added a new parameter to the speakText function called thisTag and updated where you called the function to pass a tag textAudio or textAudio2.
If it's not what you want, it's a start to solving your problem.
You'll have to move or change this function though.
+ Audio: On "textAudio" ended
-> Audio: Fade "music1" volume to 0 dB over 0.1 seconds, then keep playing
-> Audio: Fade "music2" volume to 0 dB over 0.1 seconds, then keep playing