Sounds like what you might need is a 4 or 6 channel amp that has builtin crossovers.
I use a 4-channel Sony amp that is 1 ohm stable.
I power all of my 4 door speakers with one channel that reproduces everything above 50Hz.
The rear channel feeds my 2 12-inch RF subs only the low frequencies.
The system works flawlessly and finetuning is fairly simple.
Good luck

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Black is beautiful.
'99 Contour SVT.
...always clean, always mean.
[This message has been edited by Sadeeq (edited March 11, 2001).]