A distrobution block is just that. A splitter. You can get them at any autoparts store, usually for less than $10. Usually all they are is a big hunk of brass, with holes drilled in them, and a case around them.
You should also have a fuse before the OPUS. I don't have one, so I don't know the rating, but you should even have a fuse closer to the amp too. I have one at the battery, really hefty one like 100 amps, and then back in the trunk before all my devices I have a fuse block that I use as a distrobution block.