Ask them only one question. Where do they find anything other than individual Nirvana as a goal?
Besides, leave alone Sri Aurobindo, even within the traditional paths of yoga where the final goal is an individual mukti of some kind or the other there are disagreements on certain crucial aspects of Reality leading to the different schools of Hindu philosophy. Surely there will be common elements in almost every path but there are other elements that are unique and different in different paths. Even the goal of Mukti is conceived differently, say, in the path of bhakti, karma and gyana. This indeed is the beauty of Sanatana Dharma. To say that everybody is saying the same thing is akin to a blindness that says that Sun and Moon are the same as both are sources of light for the earth or that apples and oranges are the same because both are fruits. It is only the small and narrow or the lazy mind that is happy with a superficial reading that would say that all is the same.
Affectionately,
Alok Da
