It looks like theAudi have been doing a lot of testing on the A6 based salon versions that it has refreshed. There have been a lot of spy shots of various model such as the A6 Allroad in the European spec. There are now some shots available of the S6 which is a car that will be available in the US.
It looks like there will just be a few subtle changes to the car/ The lights, both front and rear will have a few changes and there will be a few changes to the look of the front and the back.It is expected that the headlights will appeal with a new LED DRL pattern but nothing more different than that.
It is also expected that the interior will not get a great deal of changes either. The MMI Infortainment system will have an upgrade as part of this. It is hard to know what might happen under the bonnet, but with other changes seeming to be so small, it is unlikely to be anything too significant. It is therefore thought that performance will not change dramatically and there will be little change in the power of the car either.