Powerful Aura provides 5 nearby allies within 600 range any aura you recieve, and Tempestuous Aria increases the number of targets your shouts have from 5 to 10. So what should happen is that when you use "Feel the Burn" You give 9 other players fire aura, and yourself. Powerful aura then gives the fire aura on yourself to 5 more allies for a total of 15 people effected by the aura. (This is what i believe is supposed to happen)
I'm sitting in LA just spamming this on people and i don't see it hitting 15 people but i really can't tell how many people it's effecting.