Most
dtg inks are made to adhere to natural fibers (cotton, bamboo,...) and not synthetic fibers (polyester, nylon,...). The ones that I have seen done it have used pretreatment on the shirts. However, these tests using white ink have not all been real successful and the cost associated with doing these steps is more than doing a print-cut type transfer. Do a search from YoDan and he has posted some pictures of his tests.
Sublimation is the best way to print on to polyester for short-runs as it will last longer and have less of a hand. The negative to sublimation is it is a light transfer application and can't go on dark garments. However once you add the pretreatment (which is require when printing white ink), it will change the way a shirt feels and you will lose the wicking effect.
Good luck with your research,
Mark