current draw and fusing

Long Story, short.... a customer brought in an entire Sony system to have installed. (I dont usually do it, but the price was right). He claimed everything worked from a previous car, and just needed "the wires ran". After testing his amplifiers before installation, one of the sub amps had no output. He brough me a Hifonics 2006D Monoblock amplifier.

His enclosure was already made and wired up. There are 6 Sony Xplode which read approx. 1 ohm at the input.

The 2006D Amplifier claims to be 1 ohm stable. There is 4GA wire to everything, and that amplifier is fused at a distribution block for 60A (55A is recommended in the owner manual)

Everything is installed and ready to go. He comes back in an hour with no sub output.

Blown Fuse.

So I replace the fuse, and re-evaluate the gains with him there. I turn down the sub amp and have him play the system at his normal level, and then set the sub gain accordingly. Everything is ok. Customer leaves, and i get 5 calls the next day before the shop opens that he needs a fuse.

His "car audio expert" friend told him to turn it up, and before he could stop him, POP.

So I replaced the fuse with an 80A and gave him a spare. So far no calls, but I am wondering if this is normal for an amplifier to draw so much more current that the 55A recommended fuse rating becomes obsolete? Or may there be a problem with his subs bottoming out when he's cranking on it?

The fuse at the battery is only 40A, and the other amplifier's fuse in the same distribution block is also 40A, and neither one has had a problem. Only the closest fuse to the Hifonics amp.

Any insight would be appreciated.

Thanks!!