For power, you'll want headers/PLOG and DP.

Those will also deepen the sound of the exhaust, and barely make it louder. Deleting the resonator wont net any power gains, and will cause it to be extremely raspy with aftermarket mufflers, and drone like crazy with loud mufflers.

Mostly for sound, you'll be wanting mufflers. Consensus for the 3800 is Borla XS. I run headers, 3" catalytic, stock cat-back but with Summit turbo mufflers. Sounds good at idle, but is nice and quite above 2k.