Discharge whites will never guarantee a "snow white", white. Most of the time, depending on the shirt you are using, you will have a bone white finish. After time of experimenting with different brands, styles and colors, you will find which shirts are best for achieving a bright white. If you have a customer wanting that snow white look, try a discharge underbase with just plain discharge base, and a reduced finish coat of white plastisol, still very soft and you can achieve that snow white finish. I usually use more pressure with discharge to drive it in, less off contact, I love using double beveled squeegees from Xenon for discharge they keep the image clean and drive it deep without flooding out your image. Lots of experience on this board so you should pick up a lot of hints.
Mike