Really really need help. please help having trouble with my amps/subs

Hi there

i have one PDX-1.1000 alpine amp which is powering two 12" alpine SWR-1242D Subs and i then have two PDX-4.150 alpine amps powering my component SPR-17S speakers and SPR-17C speakers.

And then i have a pioneer AVH-P5900DVD headunit.

i have this in an old vw beetle and i have two normal car batteries, with a spilt charger, with one battery starting the car and then all the audio connected too the other battery.

I did have some really bad interference but have now sorted this by making a better earth and shortering the neg wire from the amps.

The problem i am now facing is that when i turn on my stereo, it plays a bit, then once you turn it up just a little, the subs stop working, or sometimes the other amp, so my speakers dont play, and then my subs will play without the speakers.

This is now really fustrating me and would love some help and advice.

All the audio is fairly new and hasnt really been used much.

i really would love to get this fixed.  

How do you have your subs wired to the amp?  If I'm correct you probably have it wired down to to low of an ohm load for the amp to handle because those subs are DVC s and thats a mono amp.  That amp is only stable in two or four ohm.