I find it odd that H&S says the 6.4 doesn't like a cold air intake. Especially since nearly every modded 6.4 out there has this upgrade. I have had no codes since installing mine. I have mostly run KEM tunes though. I wish I could help a bit more with your delima and will ask around at work...
Want to do it right? Right is relative. Dpf delete and tuner a must in my opinion. Want to open her up and see real gains (HP, TQ, Fuel mileage) then see my list of mods below. Can all be done in one afternoon by 1 guy.
You can see my setup below. I wouldn't change a thing! The debate on tuners can be nasty at times. Nobody that spends big $$$ on a tuner likes to admit if they went wrong. I have had all three of the major brands and settled on the H&S for several reasons specific to my needs (dd, towing, built...