Diablo is a brand of tuner. Think of it as hardware. They have some pre-made (usually called canned) tunes to do basics but if you don't buy the Diablo from someone who does custom tuning then you probably won't be able to get any kind of custom settings or tweaks just from Diablo.
Now, Jannetty Racing on the other hand is a tuner. I think he usually likes to use SCT brand of hardware but can also sell you a Diablo. Buying through him costs a little more but he will custom tune your car. He has a set tune he will start off with and then he will have you do some data logging and email it back. He makes some tweaks and sends you a new tune.
Jannetty has done hundreds of 5th Gens and he is one of the few I would trust personally. You can probably buy your intake from him as well. If you have questions about it you should give them a call.
http://jannettyracing.com/