I have same car as yours.. and I just did mine 3 days ago...

for the battery wire.. if you look under the hood on driverside... look deep..
there is two rubber holes.. top small one and below bigger one...
use below bigger one... but you have to cut the cloth from the inside of the car... once you cut the cloth and feel the rubber ring.. just lift that rubber ring little bit and put it through there...

for rem. I couldn't get my dash off either so I kinda sat up side down..
you know my head to brake pad. and my feet to head rest... I'm not sure exactly how to explain this but it's grey/black wire with yellow line going through... it's sealed under black rummber with bunch of other wires...

for rca line converter... i dont think it matters.. I just twisted two + from converter together. and two - together so I'll have only two lines instead of four. then just pick one of the rear speaker and hooked + to one side and - to another side... I might got lucky.. so if that didn't work for you.. then just try opposite...

oh.. btw.. for some weird reason.. I HAD to put the switch on my remote...
if I don't it wont give me a full power... but I'm pretty sure this is the correct way.. one of my friend (another same car...) did it exactly like this at the shop... (I copied from him..)