My questions are what is the purpose of a pre-amp?
2) will an external amp make my speakers sound better?
3) if I were to buy an external amp what would I buy a mono, stereo, etc?
2) no, it won't... amps "Should" simply amplifier the input signal. However, is another topic all together.. The simple answer is no....
3) in my system i have 3 amps. 2 stereo amps, and a three channel amp.
My small my stereo amp is rated to 500W @4ohms, as is my three channel amp. My second stereo amp is rated for 1,200W @ 2ohms...
My "small" stereo amp/three channel amp weigh about 50-60lbs.. my "large" stereo amp weights about 110lbs...
I am sure JohnK will chime in here, me and him have polar opposite opinions to your question.
I have the amps i have for 2 reasons.. one, because my previous 5 channel amp was being driven into the clipping region on a couple channels (indicated by the clipping lights lighting up like a Christmas tree), so i bought bigger amps... The other reason, because i wanted a big amp, and i could afford it, so why not... Right?