Just finished my upgrade from standard 6 speaker to 16 speaker system (added additional two tweeters in back that have place, but are not put in the factory).
A lot of work to put all the trims away
Wiring is simple - the most tough was to put ACC wire to the fuses and extend original cables to the front central (this part of loom I didn't have)
Front speakers are not so bad - great improvement vs standard.
The only problem is back - subs are very weak.
If you set fader to the back almost no sound is coming from all of the speaker (central rear, subs and mid ranges)
Temporarily I powered them from external amplifier but it was little improvement so I left them feeding from std Top HIfi amp.
If want to improve you have to change subs. Top hifi subs are to small to produce good bass.
I will try to put new software to Top Hifi amp, but having read opinions it brings only small improvement.