1. Look on Amazon for the kits. they are very well priced
2. The ford 6.0L, PICKUP even straight piped is nowhere near as loud as a cummins or duramax.
3. You have a 2006, this means it has 3 extra vanes in the turbo, which is why they are quieter.
4. The Cat on the 6.0L and the Air Filter are the best you can get. No reason to replace them unless they are plugged. I bring up the airfilter because guys will swap in K&n boxes and not realize they didn't get anymore flow.
5. On the 6.0L the Muffler is the restriction, so even just a Cat back exhaust will yield a nice improvement in torque.
6. The 6.0L, even straight piped doesn't drone unless you are under a load that requires your truck to be in a lower gear. My F350 is straight piped and unless you get on it hard, you don't really hear the exhaust. This is what many younger guys complain about with Ford Trucks. They want them to be loud like the GM and Ram's but because of the Turbo design they just are not loud.
7. If you look on Amazon you will find only a couple of kits, but I'm telling you, for a Ford, if you do a Cat back only, you are under $400 delivered to your door.
8. If you want to "bolt" on an exhaust then yes, buy a kit, but know this, you will need to get out the trusty sawzall to take the factory one out, Yes, You can get the pipe clamps loose, but the pipes may not come apart with out some work. FYI, if you spray Wd40 or such in the seams they do come apart easier.
You can have a local exhaust shopt do an exhaust for way cheaper, and also, you don't have to buy a muffler or cat from them, you can bring it in and just have them fab up the exhaust system. But your choice.