Well before you had a 5 channel amp running your system, and now it appears that you only have a two channel, which from the power output should be hooked up to your subs. So to answer your ? above yes you can get a cheap amp to run your other front and rear speakers, but this will not help them from distorting and also they in no way keep up with the highpowered RF amp you just installed. I would go with an amp with around 50 to 75 Watts RMS x 4. If I were you i'd couple your RF amp you have now with a RF 4 channel model at around this power. Your sound will be amazing and the amp will come with a crossover frequency selection to adjust the front and rear speakers correctly cutting out all of the low end signal ultimately lessing the chances for the speakers to distort.
Also are your front and rear speakers Stock or have you replaced them?
If they are stock you will get better sound then the deck with the new amp but if you are going for the best sound possible then replace front/rear spks.