yeah, you're on the right path. think of impedance as resistance, and ohms are the unit of measure for that resistance. the more resistance you have the less power you have, so when you cut your impedance from 4 ohms to 2 you are in a sense doubling you power.
now... does this apply to your set up, i don't know. can you be more specific on exactly what you have, and i will do my best to help.
by the way... when you run at a lower impedance, your amp runs hotter, and your signal isn't as clean. careful.