another rookie question - preamp or or power amp

I have a decent integrated amp ("decent" - to my ears). SS, 50Watts to 8 Ohms. It  has a preamp output. 

I have been looking at used power amps and preamps in the 2-400 dollar range.  

For example: the Parasound 2125 power amp, the Parasound P3

This is an OR question. Which choice will yield a better improvement,

1) if I put a preamp before my integrated so the integrated acts as the power amp

or 2) if I use my integrated as a preamp to a power amp?

It's also a choice to sell my integrated and save up until I can buy both a power amp and a preamp, but obviously I am itching to try one of the above options. 

My room is 15x13 so I am not sure I need a big power amp (big: 100Watts?)