Just put out another video on our Youtube channel with a rather interesting comparison, three stock S6 V10’s each with different exhaust. One with stock (with unknown light modification), another with stock but all 4 resonators deleted and one with a full Milltek cat back exhaust. All the sound is recorded with high end mic and should be a good representation of the real sound, sound level is alwasy impossible to convey in video but this is probably as good as it gets sound wise. 
Which do you prefer? 
And btw, lots more content for the S6 and RS6 V10 cars coming just in a few days. 