Yes. There are several ways of doing this.
Each amplifier you add to your bike, will draw additional amps.
One amplifier can be used to power four speakers, or you can add two amplifiers to your bike so that each amp will power two speakers.

If you want to use a 2 channel amplifier with 4 speakers, then it is basically just hooking two speakers on the left amplifier output, and two speakers on the right amplifeir output. The two left speakers are powered by the left amplifier output, and the two right speakers are powered by the right amplifier output.  

Left Speakers
Each speaker has two wires, a clear wire (negative) and a clear with with red stripe (positive)
Take the four speakers wires from the left speakers and identify the negative and positive wires. 
Take the two clear with red line speaker wires (positive), and twist them together and hook it to the amplifier left speaker positive speaker output plug
Take the two clear speaker wires (negative), and twist them together and hook it to the amplifier left speaker negative speaker output plug​

Right Speakers 
Each speaker has two wires, a clear wire (negative) and a clear with with red stripe (positive) 
Take the four speakers wires from the right speakers and identify the negative and positive wires.  
Take the two clear with red line speaker wires (positive), and twist them together and hook it to the amplifier right speaker positive speaker output plug 
Take the two clear speaker wires (negative), and twist them together and hook it to the amplifier right speaker negative speaker output plug

We also have a 4 channel amplifier, that will power all four speakers