Depends on how you have your tv set up. I have an optical audio cable coming from my tv to surround sound. So any content that is played on my tv will come through surround sound, including Alexa.
I am not sure, however, if you have audio coming out via HDMI if this will work. the FireCube uses a HDMI in so im not sure and different HDMI output would work. I don't know enough about HDMI ARC to know what to say.