Hey sorry for the delay in getting back to you.What's wrong with a K&N? I was just getting ready to install one.
How is the fuel consumption with the exhaust system?Personally, I think an exhaust system makes a nice addition, but I have no idea how much of a difference it makes. On our 2.5 turbo XC90, now sold, we used a REMUS exhaust system and when I returned the car to the dealership I removed the REMUS and installed the stock system, and I was shocked at how little response the car had by comparison. That was a real world test.
I recently installed a Eurosport system on my 2.5 XC70 and I think it makes a difference too. However even if it does not, I love the sound upgrade and would do it again just to get that sound. I used the Touring version and not the Sport version, because the T version is still a straight flow right through a skimpy front resonator and would not detract from perfoermance, and it is plenty of a bark the way it is.
Once you install the system, it is there under all conditions, it never goes out of tune, you never have to change anything, and the performance is there forever passively without any wear on the motor.