Same as above. Do it yourself. It seems daunting at first, but between the S4 wiki info and the two community projects for the 2.7T in the Tuning section, it is pretty simple (at least for a stage 1). The community projects are going to be the biggest help. Even the ones (like the B6 A4) not for your car are full of great knowledge about maps and logging. Read them all if possible.
Hate to break it to you but responsiveness (more power) and increased fuel economy rarely go together. Its usually one or the other, however you can find a good compromise most of the time.
Get yourself a cheap KKL cable, Nefmoto flash software, ME7check, ME7sum, and a copy of TunerPro. Here is a link to a thread with various definition files for the 2.7T that was posted by Nyet:
http://nefariousmotorsports.com/forum/index.php?topic=613.0. That is all you should need to start. I believe the 551R is the one you want (that said I'm a 1.8t guy so I have no clue really).
Sure its a bit of work, but quite satisfying in its own right. Bonus is you will learn enough to do your own file changes when you get around to modding your hardware. The people on here are great. As long as you are trying and not wanting to be spoon fed, they are always willing to help...