Speakers don't "draw power" from the amplifier. They present a load to the amplifier. Not sure what the impedance of the speakers are, it's usual stamped on them. Just replace the factory speakers with the same impedance speakers as the ones in there now and you'll be fine.
I just bought my G6 four days ago. Drove it from Buffalo to North Dakota and still have to hit up Michigan and Wisconsin before heading back to Texas. Once I get back, the stereo system is the first thing getting done. I'll be able to give you much more detailed info regarding the stereo once I start tearing mine out.
Impedance = ohms
Unless your factory speakers are 4 ohms, you might have trouble finding replacement speakers for them. If your factory speakers are 6 ohm or 8 or 10 or whatever, and you replace them with 4 ohm speakers, you may overload the amp and burn it up. I'm not sure what the specs are on the Monsoon amp. If I figure it out, I'll let you know.