Those subwoofers are 4 OHM SVC. The amp's spec is: 75 watts x 2 @ 4 ohms stereo...12O watts x 2 @ 2 ohms stereo...150 watts x 1 @ 4 ohms mono.

If you are bridging the amp, and wiring the subs in //, the amp is seeing a 2 OHM load mono. That is too low for the amp. You will have to unbridge it, and put 1 sub per channel.