i vote bass boost had it's part in the damaging of the subs.
question though as i am not sure if it was covered or not, but what setting on the Headunits EQ did you have them at? did you have the Bass turned all the way up on the head unit? did you have the loud feature(if applicable) turned on? and to what level? what volume level on the head unit where you playing at or have the amps set at?
60% seems fine to where you had the gain set. on all the amps i have used with my HU all my gain knobs have been set to 80-90% at volume 40 of 62, bass boost off and all bass HU EQ settings on flat. now i know most of yall are like WTF!!, but my amps have held up completely fine and rarely ever get warm to the touch.
hell i did an 8hr drive straight bumping and my amp was barely warm.