I've got one too. There is really only 3 things that work for the SRT as all the other "add ons" it has are for the lesser models.
1: Line lock. Locks front wheels so you can do a rear wheel burnout (awesome smoke by the way lol)
2: Lightshow. Enables multiple lighting effects using the cars headlights, tail lights etc.
3: Nav in motion. Allows you to enter addresses in the nav menu whilst the car is in motion (bypasses the nav lock). Cant get it to work in mine (Aussie model) and I am still waiting for him to answer my email about it.
Even though Nav doesn't work for me, the look on peoples faces when they see a SRT doing a massive burnout is worth it alone (although be prepared to buy new tires very quickly)
I have no affiliation with the guy, other than I bought one.