Best place to pick up speaker level inputs

2004 Acura Tsx with Nav. I cannot swap out headunit for it is one with the nav.
where is the best place to grab a singal for speaker level inputs. (no RCA Outputs)
before factory amp.
or after factory amp.

My set up.
3 Alpine MRV t320's
1 for polk components up front
1 for polk compnent in the back
& 1 for JBL 6x9's in the back from the factory the 6x9's only play bass. I think theres something in after the factory amp that splits them.
is there anything wrong with this set up

Also I want to get a Sound ate snhond3.(AUX Input) I am going to have to do this conversion. Can I pick up a signal from each of the channels from the Honda harness with this conversion. Im not sure exactly what it does.
https://shop.store.yahoo.com/logjam/snhond3navinst.html

OK that last part was a newb question i called soundgate & you cant get a signal from an input only an output.

youre gonna have to get a "line out converter" it turns a set of speaker wires into rca signals. or you can find amps with speaker level inputs. i like the alpine v12s.

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always looking for new info and willing to give it

You should get the signal after the factory amp (usually at the factory speaker locations, or at the location of the amp). You can always extend the factory speaker wiring to the loaction of your amp if the included harness for the speaker level inputs isn't long enough.