[Oak]

This is quite a big retro fit I think. I have RSE (Rear Seat Entertainment) in mine and there's a DVD player (it's not connected to the main audio system in this way) in the armrest to add, as well as the monitors and all the cabling. It is though fairly independent of the car/audio system, so possible but... I have an additional audio control panel in the rear, the infrared headphones and the stupidly rare and expensive remote control that's needed to change input.

I would not assume the looms are there to be honest - It was a rare and expensive option in the V70 (more common in the XC90) and it's a lot of work to add for very little gain

You might be better off looking at hacking the monitors directly - but in all honesty two tablets on the back of each seat would offer more functions, quality and a lot less money?