The TransLink.com.au website is your best resource for this; you just need to use the Journey Planner by entering Central Railway Station as the origin and Maroochydore (or a specific landmark) as the destination. I believe its necessary to catch a train and then a connecting bus.
There are three stations in the Brisbane CBD: Central, Roma Street and Fortitude Valley. You should also be able to connect from South Brisbane or South Bank if you're that side of town. about 10 years ago