The MSp and MP3 have very different sub setups.
The problem is not from the amp having to much power, far from it. The problem is from people not being able to tell that they are pushing the sub too hard and not making bass but distortion and that is what is killing the subs. A single kenwood 8" sub is not much bass at all when properly played but you can get more volume by increasing the volume and it will become louder but anyone with a decent ear will know it is just distortion and not sub bass.
Never use the bass adjustment at all and keep the EQ flat. The amps gains may have been set to high stock aswell.
The amp and sub are actual a good match. no issue there, it is the user.