Blowing subs happens more often by giving them clipped power, often times within their recommended thermal range of power handling. He isn't actually over-powering the subs unless he turns his amp way up, and is really foolish with the volume knob.
Unless he is going to blow them on purpose, it's pretty easy to tell when you're feeding your subs too much power. His subs will like the unclipped power much more than running a ~800w amp at full power trying to **** every last watt out of it, because it will be very easy to drive the amp into clipping at that time. Once he drives the amp into clipping, those voice coils will get too hot and melt, resulting in a "blown" sub.
T.J.
p.s. Didn't mean to LOL ya //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif I am working a 16 hour shift right now, don't take it personal... //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif