So I have now turned on immersive sound and had a bit of a play with the EQ. Putting immersive to maximum does definitely make it better. I am always apprehensive of doing stuff like this as it can often make things sound/look a little artificial. For example, high HZ TV's on with "ultra-smooth" (or whatever else they call it) setting at maximum, can produce a very interesting effect but in many cases it looks like you are either looking through a window or a 100% CGI film - both of which are not great in my opinion!
However, in this case... maximum does seem to do the trick to putting a bit more sparkle back into the sound.
I have found out where the sub is now, and to be honest, is not that great. IF you fold down the back seats you can feel its effects a little more but in songs with deep bass, it does not seem to ever go quite deep enough. I have quite a decent home audio system and know the sub should not be set up to be able to hear it over anything else. The M3 does this... but maybe a little too much!
There seem to be a lot of threads on switching out the OEM sub.
Model 3 subwoofer install.
Not sure I am quite ready for that though!