Hello,
Like you, I was looking for an upgrade. I did not have a sub, so I went out a bought one from NVX. Although it sounded great, I wanted a little more, as I am into hi - end audio (i.e. high resolution / uncompressed music).
I saw a video a few months back of a Tesla upgrade. I was blown away and made the trip the installer (that is in Virginia) for a visit. I spoke with the team and decided that I cannot do everything at once, so I had the NVX speaker removed and replaced with an Illusion Carbon C10 subwoofer. I must say that the Illusion sounded much better than the NVX.
For more info on my thought process and a video of my new sub you can find it
Good luck!