Noob needs help with car audio installation.

[Mezlol]

Hi guys trying to install new sub and amp into 2007 subaru liberty. Just want to know what the best method for this will be? Ive done some research and it says i need a line output converter installed since i have a factory headunit with no RCA outputs. If anyone knows about this stuff this is my first time and i dont want to break anything. Just want to know what i should do and go with. Also considered getting new headunit but dont want to pay over $300. My current stock headunit looks clean and has built in navigation and stuff so i dont want to lose that. If there is a way to do it without line output converters or buying a new headunit i would love to know, aslong as it doesn't sacrifice audio quality etc. I think there might be a way but may require harness adapters or something i am unsure :S but im worried there would be more splicing of wires involved doing it that way anyway. Sorry for all the questions but would it be best to just go with line output converters since it will only cost like 15-20 bucks each and i may need 2 for the rear speakers aswell. I am unsure but i do have a 4channel amp here is a link to it

GM-D8604 - Class FD 4-Channel Bridgeable Amplifier

Class FD 4-Channel Bridgeable Amplifier

www.pioneerelectronics.com

Will i be able to run front and rear speakers aswell as a sub with this setup? (will i need 2 LOC's?)
Thanks again