From what I gather the SE and Sport have 8 speakers whereas the M Sport has double.
If you upgrade to HK on the sport you still have only 8 speakers and the same amplifier.
Upgrading on the M Sport you not only have upgraded speakers but also an upgraded amplifier.
I have also realised that the Msport has a digital dash whereas the SE and Sport have the old analogue one.
There is a massive difference in spec between the Sport and Msport.