So, unfortunatly tuning the RS6 is not going to be like using EFI live. There are a number of steps you'll have to use and a lot to learn. As others have said, there is a mine of useful information here and on the s4wiki that will explain the basic workings of the Motronic 7 ECU used in these cars.

You'll then have to find 2 things. Firstly, you will need a program and suitable data cable to read and write the eeprom contents of the engine ecu. This is what Nefmoto and MPPS do. They do not tune the car, simply move information between the car and your laptop.

Once you have the original file from your car downloaded, you will then need to start analysing the file, finding map locations and editing accordingly. In essence, you have two basic choices here.... TunerPro is free and good... Winols is expensive and superb & has some very good features for reverse engineering. You can find a trial version though at EVC's website that will get you going. I'd suggest looking at some of the S4 Winols projects you'll find on here & use these as reference while you digest the information on the S4 wiki website and the mass of information on here.

There's plenty of help available if you ask the right questions, but make no mistake, this is hard and the only way to get a quick solution is to buy one. You will need a file for the gearbox - I bought mine from MTM, but others on here can help if you ask.

Once you've downloaded your eeprom, look for my spreadsheet on here and find LDRXN in the binary. This will be a good start

Good luck