Geoff, its 550w per channel so the head will deliver 550w to each cab, i have never plugged a second cab in purely because unless you were outdoors its just massive overkill.
i did get a warning when i picked the head/cab up that the head has more than enough power to blow the cones right out of the speakers so you have to be careful and not push it too hard, saying that though your eardrums would probably be gone well before the speakers popped out unless your slapping with no compression
my old band used to jam in a mates little shed, i literally had to move my cab outside because we thought the shed was going to give way lol, it didnt like the low B much at all, great fun when you can just hit the right notes to make the place you are playing in resonate enough to blur your vision.
the cab was also a big hit with the ladies as a seat, although i wouldnt know why...
