Welcome! I work in Greenwich. If you want to check out my FX50 that has a custom exhaust and is tuned, let me know.
There is no real aftermarket support on the market as far as kits but you can go to a custom shop and get custom turbo job done, etc. but it will run you quite a chunk of change. I've been quoted $10-25k for turbos, built trans, etc.
Honestly the 5.0L is great for what it is and sounds great with exhaust & tune. You're not going to take down SRT8 jeeps and the like but it's still quicker than most things on the road and looks and sounds great.