Depends on how loud you want it.
I ran no muffler and just a dual resonated tip on my 280ZX and sounded fine, with the cat still intact. No header. Was not that loud....really.
Now I have a single tip on my 280Z (no cat, no muffler, header), its pretty loud.
(edit) It has a muffler on it at the moment (I couldn't use the cell phone ) I have a flowthough cherry bomb type on it...Its pretty good, still has that "sound". I just want it louder again....so its coming off soon.
I haven't used anything but their tips, but I wouldn't run anything different. I just love the sound. This was running 2.25" pipe.