I don't think the arc means much, as I get a spark every time I disconnect my amp. I don't know of any good way around it, actually. Does anyone else know? Come to think of it, I know i've been told (and subsequently disregarded) that you're supposed to take off the negative battery cable, will that work with sparking?
If they blow at the battery and the distribution block, then it's probably something after the distribution block. How are the connections to the amp? There isn't any chance the positve cable is touching the ground or case of the amp? Be sure to actually figure out what the problem is, as the fuses are there mainly to prevent electrical fires, not save your amps.
Matthew