On an 08 your O2 sensors should compensate for the air/fuel mixture change that can occur when changing the air flow thru the engine by modifying your exhaust and or using a high flow air filter.
I respectfully disagree.
The closed loop function on these bikes is not a true Alpha-N closed loop system, like those on volkswagens for instance.
They use only narrow band o2 sensors and only apply closed loop running while under steady cruising, or at idle.
When you are accellerating, or decellerating, the ECM reverts back to a refrence table programmed in to the ECM to determine how long to open the injectors, and when to deliver the spark.
When ever you change the flow characteristics, adding pipes, or high flow air filter, you need to compensate the fuel to meet the added flow demands of the motor.
There is no way around it. You need a fuel management system. The only ones that work with the closed loop function are the SEPST, or the Master Tuner from the Turbo Shop.