Hi Toms, I have not been to ASN yet today so I'll probably repeat what the good doctor has told you.
In mid 2014 Audi upgraded the engine to the CREC code. Whilst probably being a good advancement in terms of emissions (EU6) and reliability, it also got a new ECU (Simos 16) which has not been cracked yet. So as of now there are NO STAGE 2 SOLUTIONS FOR ANY EUROPEAN S4 or S5 BUILT IN 2H 2014, ALL OF 2015 AND SO FAR IN 2016 (I think production has now stopped). So either you want a 2012 to 1H 2014 car or like us you'll have to take the risk and hope that a tuner cracks the ECU. There is a tuner called MRC in the UK who has stated that they are "working on it", however there's no guarantee that it will ever be done.
There are several German tuning houses including ABT but they are usually quite expensive, especially if they offer the "piggy-back" solution. If not you should be able to find a local independent garage who will tune your car with one of the "off-the-shelf" solutions from tuners such as APR and REVO. For the stage 2 they usually recommend fitting the smaller supercharger pulley. However the tuner that seems to have had the best results (and publishes "real" tunes on their FB page) is MRC. Their stage 2 uses an oversize crank pulley. In some respects this is a better solution because the OEM crank pulley can fail (the vibration damper part). The theory is that the damping is not really needed, however it is now possible to get a Fluidampr oversize crank pulley to play safe. As I noted MRC is based in the UK however they have links with other tuners in Europe (well at least one - KSF I think). Their tuning "genius" Mihnea is originally from Eastern Europe (Romania IIRC) so if you contact them directly you might be able to arrange getting a tune done locally.
As to the car I imagine your research has already uncovered problems with the s-tronic gearbox? Getting a manual is an alternative but I have heard that they can have clutch problems. The s-tronic DL501 is on its third generation (although some might say that there was a "1.5" and now we are on "2.0"). Now whilst there are plenty of owners of early cars who have NOT had gearbox problems, unfortunately those who have had them have tended to had them painfully. So it is worth avoiding the early cars, however since you already stated you want a facelift then you will. However I am not sure exactly when the latest gearbox went into production so if you start looking at one of the earliest facelift cars then you might need to check.
As to options, since my car is nearly fully loaded I am biased. I like all my options. Your issue is that since you are buying used you might not be able to find a car with the options you want. A good exampled is the sports differential. This is a fantastic bit of kit and capable of removing all understeer and even pushing the car into oversteer. But it is certainly rare in the UK - not sure about where you are. If you want advice about any of the options then ask as I probably have it. The notable ones that I didn't buy is a sunroof (I live in the UK!) and the TV tuner (I thought about having it but in the end decided it wasn't worth the money, and I haven't missed it - I didn't watch TV in my B5 S4 much).
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