Some fairly obvious info that would help provide an answer;
How big is your tank?
What is it stocked with?
How long has the FX5 been running?
Is it the only filter?
Is the entire tank new or just the filter?
Without knowing that, I'd suggest you cut back on feeding as much as possible (perhaps even relocate some fish if possible, especially if they're sensitive to ammonia) and give your filter time to establish properly. The best thing to do would be to borrow an already established filter from another tank to help with the ammonia while your fx5 establishes, or even borrowing/swapping some of your media for some from an established tank will help. Buying new media will do nothing as it won't have any bacteria on it. Maybe talk to your LFS and try buy some media out of one of their established tanks if you can't get it from a friend or another of your own tanks.
You can use all the bottled products you like, but IMO there is nothing that competes with time when it comes to cycling a filter. Patience is a virtue...