Ouch,
I feel for you there Yves, frying your command station must have been hard to witness. The fact that it didn't detect the short and shut down is a matter for concern though, if the command station didn't detect the short the chances are that a PWR-56 might not detect a short either leaving you open to frying that as well. What size are your dropper and bus wires?
Seeing as your not inclined to use the PWR-56 for the repeater function (indeed I don't know how well that would work with several placed together in the same spot) and they will all be in the one location another option would be to get a beefy 15v regulated power supply instead and run your 4 sections from that one supply through 4 separate quick action breakers.
A power supply like this would be good (I have one and it is good)
http://www.ebay.com.au/itm/390974735803 . The breakers are another story, one that I have not looked into.
- Tim