If I was to get a s550.2 and two sets of pioneer components how could I wire them? If I was to wire them in parallel I would get a 1ohm load.

why do you need 2 sets of speakers. why not get 1 really good set? 

I have room in my doors for 2 in each and the ones hooked to my headunit aren't loud enough

Probably because they are running off of head unit power

One good set on an amplifier will be good enough. Make sure you deaden those doors, great performance will come from a great install.

I wouldn't run my doors at 1 ohm, power is not that hard to come by.

Maybe I'll just get one set of really good components or 4 8ohms speakers

Sound deadening will bring any set to life, just look for a decent, reputable set and worry about HOW you install, not WHAT you install