Sounds like it could not enough ink or pre-treatment, print a test file onto a sheet of transparency, you should get so much white it will pool. If this the case you need to work on your pre-treatment methods.
Don't be misled by the rip saying default, you need a profile for every different kind of head & the printer it is used in depending on the ink brand. You may need two passes of white with that printer which will require perfect rewind registration.
Also if you have the white in a CISS or standard carts it will need shaking on a daily basis as the white ink splits in the pipes giving a low pigment (dull) print.
You should get some help from the seller as they should have experience in that specific printer and do have a duty to support you or they should not be selling it.
Hope this helps.
Colin