Hi guy,

Don't get too wrapped up in a quest for horsepower. These motors aren't the most supported platform and Mercedes choice of electronics (MAF & various monitoring systems) have greatly limited any potential for easy modification. You would do better to focus on handling and appreciate the car's amazing mid RPM torque. Maybe spice up the exhaust note and drop it a conservative 1.25" to complete the image.

And ignore the typical "8 hp gains" from things like intakes and underdrive pulleys. There are cars that gain 20hp when the sun goes down (like my turbo dodge), the NA crossfire's intake is about as COLD as you can get it (right at the nose) and 8hp isn't worth the time it takes to swap the pulleys... not to mention the reduction in power to your interior accessories.
ECU upgrades seem like more worthwhile mods if you don't have to worry about voiding a warranty.

... Then again if you don't have a warranty, I'd be saving every last penny for when the German engineering wet dream turns into a maintenance nightmare.

Good luck and happy motoring.