bose head unit with aftermarket

I have a 2000 Nissan Maxima that I have been playing with for about 3 years. I added an after market amplifier and many subs over time. I took input to the amp from the input to the stock subwoofer. Ran that through a high-low pass filter and into the rca inputs on the amp. It works sometimes but sometimes I feel like I blew the hi-lo filter or am not getting proper input levels. I have heard hundreds of stories about the bose system but I would like to use the stock stereo. How is the best way to get all the sound info from the stock deck and what do I need to do in order to change or filter it before putting it into an aftermarket amp?

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Realist of The Reals

u should tap the signal off the factory amp

Thats where I've been getting the inputs but I have blown out channels( or maybe just a cheap filter) on my hi-lo filter. Is there any particular component I should be using to filter the stock amps outputs before going into my aftermarket amp?

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Realist of The Reals

you can mess around with the mtx reQ.

Why do you want that factory hu that badly? The maxima is an easy car to change out the hu.

I didn't want to get into changing out all the stock speakers. I have heard from many different places that you have to change out everything or nothing. I like the stock door speakers, well they sound ok is what i mean to say. Do the stock door speakers work with any aftermarket stereo?

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Realist of The Reals

There are two ways to get above average sound from your factory deck after the factory amp. The first is to use an Audiocontrol LC6. This will accept your speaker outputs from your factory amp as high voltage balanced inputs. This is superior to the after market single ended RCA type signal. Many people will yell just because I said that but they frankly don’t know what they are talking about. The problem with using the hi-low converter that you mentioned is that typically the signal is dropped by a factor of 30. This raises the noise floor and limits your amps output. Again many people will not like that statement but an amplifier is actually a multiplier. It can only multiply the signal that you give it. Also hi-low converters have isolation transformers that create delay as frequency rises.
The second and best way that I know of to interface your factory deck is to use a Zapco DC series amp. These amps ship with the ability to accept the high level balanced input that your factory deck already supplies. And like I said it is superior in design to RCA. As a big time bonus these amps also contain the best DSP (EQ, time delay) on the market. You can get all that and a bag of chips out of your factory speakers!