On the subject of possible hearing loss as a result of adding a subwoofer to the mix:
1. Sub installs are generally in the trunk.
2. Sub frequencies are in the order of 80 Hz and lower. The lowest frequency spectrum is "felt", not "heard".
Most hearing loss is in the prolonged exposure to the higher frequencies, not bass. If you ever left a rock concert or dance club with ears "ringing", it's from those large tweeter arrays and midrange horns, not the bass drivers.
And for this particular application, retaining the OEM setup is a sure bet that there will be little to no added hearing loss...
