They only showed three, obviously not counting hashirama that leaves two. Naruto & Asura, so yeah thats why i said all, more accurately all asura incarnates we've seen."All asura incarnates were shown as kurama jins" We only saw two with Kurama...
Hagoromo himself said that down the road Ashura had awakened the power deep inside. Both Indra and Ashura in this case were born with equal power. An avatar is made from chakra. Indra created Susano'o with his own, and there should be no reason why Ashura wouldn't be able to do so. Seeing as how he took on his father's approach to things, he probably became a natural sage. There's no way of telling if the orbs were Truth-Seeking Spheres or some other sort of bomb. Not to mention that the heads do not represent Kurama at all.He obviously has because he possessed kurama chakra mode & gudodama. He was obviously a jinchuriki because he needed the power to match his brothers natural talent(visual prowess). Unless you're telling me asura suddenly mastered every element and gained his own chakra avatar + gudodama and sage mode on his own, this would defy his entire character.