Softbox grids

Hello all, I am using a 24x32 Photoflex softbox for on location portraits and been getting very nice lighting results, but when outdoors I have noticed trying to achive broad or short lighting is not working out to well. Just wondering if this can be achived outdoors or not and was also wondering if box grids would help or not? I power box with 580ex II or if needed I have made my own dual flash bracket and can use my second 580 II if needed for more power. Also want to know how grids change lighting from box and how it will effect background and shadow. Thanks.