Have a chat with Jason @Absolut5 , he will give you great advice, and supply or supply & fit many different upgrade routes if you wish. Given his professional raison d'etreis are Transporters & Audio he kind of ticks both boxes. There are quite a few speaker only upgrades, I went the component speaker upgrade and front amp with sub route, and it sounds unbelievably good; even after having it fitted for a few months now, I am still really impressed when I jump in the van. Not only mp3/iphone/sdcard/cd/spotify music, but even the plain old fm/dab radio experience is improved beyond all expectations.
Seconded.