yeah i think its just a new live wire from battery that may be required. doe to the 4x60watt. could just be manufacture covering them selves. but 1 wire from battrey shouldnt be to hard should it (famous last words)_
All you have to do is run a new power cable direct from the battery and a new ground.
The new power is due to the power that the head unit uses as many of you have said. The new ground is becuase the thickness of the power wire has to be the same or greater than the power cable in case there is a surge. In which case the original ground would have melted.
And yes 50w x 4 head units are unlikey to require direct power feeds, as a basic rule direct feeds are required for 60w per channel + head units.
If you've got space on the plastic cover that runs down behind the handbrake, you could mount the remote there so that the people in the back could turn the volume up if they so desire. I would mount it on some velcro just in case you want to move it around.......
I had one with my JVC. The only use i found for it was finding rattles without annoying the neighbours. As it gets about 5 times louder when you have to open the door when its soundproofed.