I currently have front and rear speakers in my 6n2 and have a set of 6x9 and s parcel shelf with holes in lying around. Thought I may as well put them in but where do I wore them into? The head unit has rca for front rear and sub but the speakers arent connected by rca cables. Any ideas how to fit these? Cheers!

You'll have to run a pair of wires from each 6x9 and connect them to your rear speakers or behind the head unit. Just tap into the rear speaker wires behind head unit so left 6x9 to left rear speaker wires and right 6x9 to right rear speakers wires if you do it this way your balance and fader will work as normal.

Having two speakers run in off of a wire meant for one could Make it loose quality and distort it couldn't it?

It will be fine mate but the proper way of doing it is adding an amplifier and connecting 6x9 to amp.

Agree with Riz. I did this but found the head unit was sufficient to run my rear 6x9 JBLs. It's a very good head unit I might add, so maybe that may be the reason.

I'll be reverting mine back to normal soon so the power amp (Rockford Fosgate) and 6x9s will be removed and sold, since I also upgraded the front speakers (to Pioneer) and find an imbalance (different brands) in the sound. Too much bass in the rear when I try and turn the bass up in the front

Personally, I wouldn't bother with them in the shelf. I would run a small subwoofer in the boot as usually gives way better balance and actually adds to the sound as if it's tuned right it will add more low end bass. Adding more speakers just makes more of the same noise and having them pointing at the roof behind you doesn't do much for sound stage.

That's said, replacing the front door speakers with 6x9 speakers is surprisingly effective. They are cheaper and usually can handle a lot more then cheaper 6.5" mid drivers. You would have to make a custom mounting though so may not be worth it.

Running them in parallel with the rear speakers will increase the resistance and you will loose power to each speaker. The head unit will usually deal with it okay but it's not ideal.

I decided against it now as quality is good enough. I got a 12" sub and upgraded all the speakers.