No i don't recommend anyone change the header any more, particularly on an automatic, its not worth the hassle and the auto's really benefit from the the low end TQ the stock manifold gives.

if you want to keep the sound no louder than it is then i would keep the stock S and Mid pipes.

I would also recommend a "rear sway bar" but i think the auto already come with a stiffer one than the 5 speeds.

 

I did the complete TRD suspension, springs, struts, shocks, swaybar, alignment, enkei 18" wheels, Pirelli Pzero Nero tires, full body kit with rear lip spoiler, hotchkis front strut bar, monster motorworks rear strut bar, all done before the car had 250 miles.

Did I forget anything, oh yeah she is scheduled for 2- 2 hour track sessions at Moroso Motorsports Park in October, high performance driving school.

Modify car, modify driver.

 

Wow nice.

looks like she is all set.

you may be able to free up some HP swapping out the S-pipe and Mid-pipe for a 2.25 S-pipe and 2.25 catless MID-pipe and still keep the sound levels down by using 2 20" perforated core straight through mufflers on the mid pipe.
the gains would be in the High rpm range thought...