Aniroodh Sivaraman, 

Go beyond the subtle body?

This sounds like Buddhism to me. Or perhaps advaita vedanta. Check the Pali canons for a method. For inSelf Yoga it is sufficient if anyone could remain on the astral levels, the favorable ones, and not have to be physical ever again. Doing anything beyond that is fantastic. Who knows if it is practical?

Testing to see if one can live only on the astral levels is easy because one access those subtle places in dream experiences and one can test oneself to see if one would be satisfied living there forever and would not need the fulfillments one gets from physical reality.