IF the amp is not stable it will shut down.

Many things it could be.
Crappy amp.
Crappy box. (usally #1 issue) the box will make or break a sub.
Bad Crossover settings.
how you internal wire the sub? was it SVC? DVC? ( all that will do though is tell the amp how many watts to push)

Now when you say sounds like crap just loud and boomy? That is what L7 is good for
Does not sound clean? You got the wrong sub.