Some pictures of my Helix sound system and Fender speakers. The Helix system is from Golf/Polo, but can be fitted in the up, without problems. Still almost plug'n'play (some adjustment to pin configuration in connection to radio).
The Fender speakers fit in without any problem, here the pins on the connections has to be moved in front speakers, and new connection house to rear speakers.
Realy like the solutions, plays very well. Treble units (think they are called so) are standard, Fender does not fit without an crossover filter of some kind.