Not sure if new filters add any power or not. I have seen applications where they do not.

EvoSport has some dyno's showing the SL55 y-pipe adding a couple of ponies. It is not a huge gain but it is something.

The Y-Pipe is the y-shaped pipe that connects the two air boxes to the TB. If you look at the stock version it is very small and restricted. The SL55 has a larger y-pipe that run ~$75 from an MB dealer. It is not a direct bolt on as the tubes are larger but an adapter is easy to make from either silicone couplers or your stock y-pipe.