Buy a replacement panel filter, they're a little more free flowing. You should notice a difference in engine note and maybe a touch more responsive but i've not done anything like this on a modern car. You could always drill some holes in the back of the air box to make it even louder still...
I fitted a universal cone filter to my 205 and it made quite a bit of difference - well worth it, but then again it is an older car so probably benefits more.