I noticed that the speaker cables are fiber optic!? How easy is a speaker for speaker switch out
I’m 99% sure that the speaker cables are not fiber optic, but the signal from the head unit to the factory amp is a MOST network (aka fiber optic). So, in terms of switching out the speakers, it’s pretty straight forward. The difficulty is that the stock system just uses one set of speaker wire from the factory amp into the door, it then splits inside the door and each speaker has it’s own passive crossover network attached. Depending on if you have the upgraded factory set up or not (quickest way to tell, do you have a center speaker?) will determine what your factory set up consists of, front doors have 6.5″ woofer, 2″ or so mid (if you have the upgraded system) and the tweeter.
Most 6.5″ woofers will fit as long as they are not too deep, the midrange are a bit of a headache as they attach directly to the back of the door card and due to the lack of room, there are not many options available. I have used both some Infinity Kappa 20MX in that spot and now run AudioFrog GS25’s (I suspect the GB25 will also fit, but they cost twice what the GS25 do). Replacing tweeters is a bit fiddly as the factory ones are plastic welded to the grill, I had to carefully drill out the welds, dismantle the entire thing and then with some screws and glue fit my replacements. I have also seen others mount tweeters either fabricating entirely new sail panels with fiberglass or cutting an opening in the factory grill and having more of a surface mount. I wanted everything in mine to look stock.
I could do a complete upgrade with keeping the original head unit in place that would be cool also!
Complete upgrade while retaining the factory head unit is entirely possible, in my case I use a Helix SDMI25 to grab the MOST signal from the factory head unit and then TOSLINK into my DSP. You can read about my upgrade here Volvo V60 – Audio Install Log Be prepared though, if you are doing a complete upgrade, you might have to take your doors off (in order to run additional sets of speaker wire if you are running active crossovers) and take windows out (in order to fully sound deaden the doors) 
Being able to use Carplay (or Android Auto) for us with earlier P3’s is possible, but involves replacing the factory head unit. I keep toying with the idea of replacing mine, but am undecided. There are a couple of threads in the S60, S60CC & V60, V60CC (2011-2018) forum as well as some in this sub-forum with details.