Hi Ahmed, thanks for asking in the forum than PM it just that this way will help everyone like you when they need it.
To be honest apart from small glitch of blip (cut-off) at very high volume, which sometime is irritating I haven't found any sane reason to add amp and sub. And to counter this blip, I found an easy way out to adjust fader to +4 or +6 for rear in a setting of 15 point so that I can hear more from the back and this resulted in a real solid thump from the back that is loud enough to shake my seat backside. However this setting another drawback is in low volume you will miss the front impact so I keep playing with fader as needed. You will understand this and master this if you go with my type of set up. Actual reason for this blip (I think) is front is 60W and rear are 100W and head unit pumping at 100x4. If I play only only on rear then this blip is not there.
In my case it was a space trade-off with this little inconvenience, so I chose the later as my Pajero being off-road ride, I want as maximum space as possible and I don't regret this choice till date.
If you like to hear this set up, feel free to pass by anytime and that will help you even more in understanding what I am explaining.
Both shop who installed head unit and speaker did't do a good quality job, so don't go there. Instead if you like buy above speaker, head unit and cables from souq or any mall and get it installed with proper sound guy. This made a big difference in my case when I scrapped all OEM wires at Barry's workshop with new cables. Started hearing every little detail as much as my hearing sense can absorb. Proper installation with good cables were amazing and way better than stripping wires and twisting and taping them so many times. Hope it helps.