I just edited this post by eblade, and stickied it. I think you'll find it helpful:
www.poolforum.com/pf2/showthread.php/24529

BUT . . . I strongly recommend that you go ahead NOW and order Unicel cartridges, and learn to manager your pool as is. The sand filter is not a fix-all. If you haven't looked though the Simple Recipe page, I'd recommend doing so: http://pool9.net/ssr/. You may want to get the Unicel, drain, and restart using the SSR.

You may also want to consider ADDING the Intex filter, rather than replacing the Pro Series one. Either way, I think you'll see that the conversion is a bit more involved than you imagined. Draining and refilling, following the SSR would allow you to enjoy your pool this year, as you work toward replacing or adding to your existing filtration.