I think your missing a critical part of those stats. There is a symbol beside the numbers, that looks like the omega symbol. Its known as ohms. When the ohms go down from, say 8 to 6, the power output of an amp usually goes up because there is less resistance on the amp.
To answer your question the amp is capable of putting out 100 watts of power if the speakers are 6 ohms (impedance).
Also power is a logarithmic scale, which means that with each watt of power you add the benefit decreases by a certain amount. For example the S30's are 90db sensitivity. This is usually measured at 1 watt of power. If you give the speakers 10 watts of power if will add 10 db of volume, making the volume 100 db, if you give the speakers 100 watts of power it will only a total of 20 db of volume which means that it will produce 110 db's. To add another 10 db you would need to increase the wattage to 1000.
See how it takes so much more power to get the same db increase with each step?