let me ask you this, if you can answer alot of things will be cleared up.....

are your subs single coil or are they dual coil? what impedance are they?

goin from the website u pasted the subs are single coil 4 ohm. thats what i gather anyways, it doesnt even say 'single coils', it says MONO 4 ohm, from MONO i get they are single coil. if im wrong correct me.

how and WHY u'd wire that in series-parallel is beyond me, thats like the worst possible way you can wire 3 single coil subs. u'd get two subs getting no power and one getting all the power from the amp.

what you really need to do is ditch those crappy amps and get one thats 1 ohm stable. normally a single channel, class D amp. the amps u have now do not match/work well with your subs.

 

^^^ exactly what he said...single mono amp that is 1ohm stable will cure your problems. I'll assume your subs can handle at least 300 watts rms each, so wire them parallel...1.33 ohm...get a 1000 watt rms class d amp stable to 1 ohm and you'll be happy!!