I dont think you are over powering them, unless they are 100 watts rms and 200 peak. I have 2 XLC 15's with a Punch 250a2 on each. One amp puts out 392 watts, the other 403. It took about 30 minutes before I fried one of them.
I'm not sure how the channels are on the 4 channel amps, but you should be able to mono each pair of channels to get a 4ohm mono output on each.
If your are bridging both woofers off one set of channel and you have 2 4ohm woofers, you have put the amp into 2omh momo, the amp isnt stable at that load, it doubles the watts but overheats the amp.
Hope this helps.
PS. My system hit 142spl with the windows up.