whiff42o

Ok here's my problem. Whenever I turn up my Head unit (New Sony Xplode) past a certain point my amp will shut off. As long as I have my amp turned pretty far down it wont do it. But I feel like I'm being robbed of the potential of my speakers. I thought that maybe it was the amp so I took my other amp out of my other car and it did the same thing but even quicker cuz it's a 900w Lanzar and the other one is a American Pro 600w. I've checked all of the connections way to many times and never found any problems. Someone told me that the ohms has to match up on the amp and on the subs but i've never heard of that. If any one has any ideas please let me know i would appreciate it very much.