You won;t need a programmer to run a slip on with your 550. They run rich anyway. The bad news is you won't gain anything by adding an exhaust except a different tone. To get more power to the ground with an exhaust you need to replace the whole thing, not just the muffler. As far as I know there isn't a aftermarket full exhaust system sold for the 550. Also, more air out, means you need more air in. A more free flowing air filter. You really want to get crazy, cut a hole in your airbox and install some frogskins. More air means more fuel, which means you potentially need a programmer.
On my 550 I run a HMF pipe, K&N filter, I cut hole in my airbox and installed a TwinAir vent, and have HMF optimizer programmer. All those things were a waste of money, although I do think it sounds better. I disconnected the programmer, it was worthless. I would not waste your money. If you do get a programmer, I think Dobeck makes a lot for others to put their name on it.
If you haven;t already, get a clutch kit. Best thing you can do for more lower end grunt you are looking for. QSC is what I run. Highly recommened on this board. Ridinagain on this forum is a dealer.