Forget paying a grand for a Brabus or Eisenmann axle-back. That's plain obserd. I went with a stainless/polished Magnaflow axle-back (#15615) for $140 (my buddy owns an auto parts company and will give you a deep discount if you are referred from me) and replaced my stock cats with Magnaflow metallic-spun high flow cats (#59959). The tubing is already stainless and mandrel bent, so no need to change that. My total cost for the exhaust installed was at $500. Way better flow and sound (look in My Garage for pics installed).

As far as the intake, they're already optimized for maximum flow from the factory, so just change out the panel filters for some high-flow filters. I went with K&N at $80/pair (just don't over-oil them when you clean them). The cone filters with polished tubing are just for asthetics since they draw hot air in from the engine bay.

Tuning is another option. I contacted PowerChip Group and found that they can "overtune" your ECU beyond the engines parameters cause irreversable damage. I asked Travis there about that and he would not give me a straight answer. That tells me not to go with them. I went to a local Bosch service center and got a custom tune based on my mods and within the parameters of my 2.6L W203 engine and gained 15bhp and 18ftlbs. I use 93 octane. Next up is a pulley. I hope this helps!