There is oodles of talk on many forums on this done to death subject! and you will always get various opinions on the pro's and cons!
I could rattle on about this but i wont, in simple terms, you won't get any performance gains that you will notice (but you will get many say they can 'feel' a difference !!)
Keeping the stock airbox but with a more free-flowing filter is the sensible and simpler option.
If you want to go the aftermarket option, then make sure you go for a Cold Air Induction (CAI) filter housing ( i guess as you have mentioned the BMC Carbon kit, then you know about this?)
One thing you will get with CAI on the V6 is a wonderful induction roar at mid range and above, This alone me be worth the conversion
Finally, i have fitted on my V6 a Ramair fully enclosed stainless housing with internal foam filter and extended air induction hose low down behind the front valance.
I can give this my full seal of approval!!...I have only yesterday come off a rolling road Dyno' and my 12 yr old, 100K mile 2.5 V6 is producing exactly 187 BHP (remarkably, this is the exact manufacturers figure for this Arese engine!!...No loss at all in power! ,Well pleased