He has info to go on. If he chooses to do anything with it is his concern. I figure if he has any more questions he'll ask. If he chooses to do nothing with the info, his problem.
The problem you are having is in no way related to the power handling of the subwoofers in relation to the power output of the amplifier (not that the 100w difference would make any difference in performance to begin with). So forget about that.
Look into the things mentioned already in this thread....the gain setting, the possibility of loose connections, etc. Forget about whatever the installer told you and follow the advice that has been specifically given here in this thread.