Whilst I much prefer my 2014 Sport to my previous 2013 S, the S exhaust definitely made a better noise with standard exhausts on both
Yep, that's exactly what I found going from 2011 S MC-shift to a 2013 Sport MC-Shift. The noise was slightly lacking in comparison. The x-pipe was a must on the Sport for me, but not necessary on the S.
I do think there's a couple of reasons for this.
I'm sure there is better sound proofing on the Sport, as the road noise is definitely too, so would effect the exhaust sound getting in the cabin.
The software on the downshift blip is definitely less aggressive. I have found that if you let the revs drop a little lower, then double tap two gears down on the sport, you get the same effect.
Also, the newer car is, well, newer. So the exhaust is newer and in my case had covered much less mileage. I have definitely found, now I have put plenty of spirited miles on it, that the mufflers are loosening up and the sound has improved significantly.