Ok for the info on V6 duals... make haste to --->
http://www.mustangforums.com/m_1183819/tm.htm
I am pretty sure that all the knowledge you seek lies within...
Also since it IS your first mod... for future reference
GO HERE --- >
http://www.mustangforums.com/m_2147886/tm.htm
I would personally go with an H-Pipe and the sound mufflers of your choice (not sure what kinda sound you want).
I have a single MRT Aeroturbine... some say it sounds kinda ricey at higher rpms but I love it... it sounds more of a euro road racer at the highest rpms. Going through one of the tunnels here in town, I scared the hell out of about 3 cars when I punched it at the green light through the tunnel... I even saw a car swerve in the rear view mirror when I passed lmao. It wasn't intentional, but I did have my windows down and just wanted to see how loud my car could get through there :P
It has a nice muscly rumble to it at idle or normal driving.
Here's a link again for mine... This video has the most closest sound to what it sounds like in person. It is that deep and does scream when it's at WOT.
http://www.youtube.com/watch?v=fLlbWScTjSM
That was for the single MRT... don't have one for duals...
For other sound clips click on that first link I gave ya!
For a whole H pipe w/ mufflers setup you are looking at FROM @ around $450. Someone just got a sweet deal in here on their Duals (JBA i think they were). I've since checked out numerous sound clips on those and they sound pretty damned good. They aren't the most expensive of the crop either.