The engine in the CX-9 is not the same as the MKX. The MKX got variable timing on the intake and exhaust valves whereas the CX-9 has it on the intake valves only. The CX-9 makes about as much horsepower as the most powerful version of this engine that was installed in any other car, it's down a couple of horsepower to a version installed in a Lincoln MKZ I think.
There is basically zero aftermarket for these cars. A long time ago Borla made a catback exhaust, but it's long since out of production. I am unaware of any aftermarket ECU tuning options. There are a few people who drilled holes in the air box, but this may just make more noise than power.