Pull the power from the battery through the bulkhead behind the glove box... need to take it out but it isn't hard, only a few screws.
I pulled the seats and carpets out to run the cables back, but I had to re-wire my car... was much fun, but you can run the cables down the side of the car without to much messing around.
As for the 6x9's I'd sell them and get some 6x4's as thats whats already in the car (unless you have holes cut already)... but thats just me, easier and looks nicer to (well I think so).
I'll be taking my 2 10" subs out at the weekend all being well, so I'll see if I can take some pix... nice 15" going in