if i have a 500 w. amp at 2 ohms/250 w. at 4 ohms...then can i safely use one 4 ohm cab without a problem? If yes, the rig will be running at 250 watts, right? Can I then later add another 4 ohm cab - let's say when i have the money? If so, the rig will be running at 500 watts, right? As you can see, i don't get ohms/watts/etc. very well. So, any help is appreciated. Thanks.