Humm... I personally don't hear of an aggressive from most Flowmaster pipes with muffler only setups, but its all a matter of taste.
I have a GT with what may be one of the most aggressive axleback (muffler only) kits available, the MAC Boomtubes (only the SLP Loudmouths are louder/angrier in my opinion, which are basically a straight-up muffler delete.)
The Boomtubes are a muffler delete with a minimal amount of muffling in the tubes that eliminates any "airy" or "raspy" sounds and produces almost pure engine music without any filler. They're incredible. My car is completely stock and everyone who hears it thinks I put in some kind of big block monster.
A V6 obviously is not the same as a V8, but I have heard some pretty killer sounding V6 engines in my time.

I don't know if the Boomtube for V6 would be your thing, but I liked the way it sounded.
Along with Boomtubes, I would YouTube search Mustang V6 (make sure the year is 2005-2010) with each of the following brands: Flowmaster, Magnaflow, MAC, JBA, Ford Racing, Borla, Bassani, SLP, Pypes. I would also search "V6 Mustang custom exhaust" and find videos with the right year.
I strongly recommend doing a lot of research and really shopping for this, I took almost 4 months to pick my exhaust and could not be happier.
Its a very simple install, just take the old muffler off and put the new one on in its place. About 4 bolts total.