i don't have much experience at all with direct-to-garment printing, let alone doing it on tricky fabrics. my understanding is that since it is such new technology it still hasn't quite been perfected across the board. i know the light colored cotton tees are superb, the dark colored cotton tees are coming right along, but i would avoid doing it on a touchy expensive fabric such as a rash guard or a team uniform/jersey.
were you having issues on both the shorts and the tops? i use different ink blends on the rash guards as i do on the shorts.
if you have no other choice (i.e. no manual or auto presses), than i would ask wet effect for some fabric swatches - which they have plenty of - in order to test out some different inks and ink formulas without the risk of damaging an expensive garment. look into additives.
your ink selection will be the most important part here, so shop around and see if you can get some samples from different manufacturers. you'll need to find something with a super high opacity, extreme flexibility, and excellent resistance to dye-migration and ghosting.
if you don't have any luck, by all means we would be happy to help take care of the printing for you - the items can be ordered through either wet effect or myself.
don't hesitate to ask if you have any more questions - i ran the gamut when testing/perfecting the printing process on these fabrics.