I've been thinking about replacing my amp head with a Carvin BX600. however, there's nothing really wrong with my cab, but im not sure if the impedances work or not, or even know what they are for that matter. my current head 125w @ 8 ohms, and the cab can handles 200w and has a 8 ohm impedance.
So, goin’ down the Amazon in a light green ’57 Chevy, uh. Well, you think that’s, um, kind of heavy?
Well the BX600 puts 225 watts into 8 ohms, so as long as you don't crank it too much, you should be fine.

Though I will suggest that if you have "spare" cash, pick up a BX1200. Its basically TWO of the BX600's power amps. Meaning you can run it into one 8 ohm cab and get 225 watts, but you'll be able to expand it to up to 1200 watts if you ever have the need.

As for a real explanation of impedance, check the FAQ.