You're right, and after a bit of research (which I should have done before saying it wasn't necessary), it's obvious. Here's a link to a good explanation on the subject.

 

Ok then we do need a crossover.

 

I guess it's that or really large diameter exhaust pipes

I'm going to give this some more thought to see what type of exhaust coupling I want to put into this system. I'm currently thinking that I might want to fabricate the traditional H as well as an X and to try each with straight pipes before I make up my mind, but to do that, I'll have to wait for warmer weather.

 

Dual in/out borlas! they sound soooo nice.

 

I would like to know which gives the best performance, either the H or X pipe. You might not think it makes a difference but it does. Some engines perform better with one and not the other.

 

X pipe better top end power
H pipe better low end torque
Either way you need one, without them it sounds really annoying like a farm truck with glasspacks. Pap Pap Pap Pap

I had an X pipe on my dual system, it's a sound you can not re-create with a single exhaust, really nice.

 

So, can you get a dual in dual out muffler with the crossover built in or does it have to be closer to the engine?

 

Yes you can get a muffler with a dual in dual out with built in X from gibson. http://www.gibsonexhaust.com/cftmufflers.html Now as far as how close it needs to be to the engine I have no idea.

 

Here's an article with a lot of information to digest.

 

Here you go.
http://www.youtube.com/watch?v=eTmNzBD7u2I