yes this is okay because your amp and many others run at a minimum of 4 to 1 ohms it depends on your amp if you are running a bringe then it should be at least 1 ohms if you are running it on mono then it should be at least 4 ohm
the difference is the power thats running to the sub and how the power is running im guesing that your sub is not hitting as hard as it should
look on the back of your amp and make sure that your amp is capiable for your sub
most kickers are made to run on mono wich means you only have one output channel on your amp
there is no way to set the number of ohms it runs on you can only hook it up incorrectly or correctly
if you want your sub to hit like it is suppose t then make sure that it is a mono amp that runs it