curious question about wiring

[skeurton 10+ year member]

i have a mazda 6 with a bose stereo. the bose amp is underneath the passenger seat. it runs to the four cabin speakers and has a preamp line running to the bose sub, which has its own amp. all the speakers are 2 ohms.

now, what i would like to do is install another amp without removing the bose amp. i would like to use this for other audio devices (laptop, minidisc, iPod, etc.). so here's what i was thinking...

-use a 4-channel amp with 2 RCA inputs and 1 RCA preamp output

-split connection from laptop, MD, or iPod into 2 RCA connections to run into the 2 RCA inputs on the amp

-run the speaker wires from the amp and splice them into the existing cabin speaker wires

-run connection from the amp's RCA output and splice it into the preamp line going to the bose sub

is this even possible??? if this can work, then the head unit would not even have to be on when using other audio devices. plus, i could put a switch inline to the amp so that i can turn it off if i decide to use the radio. it makes sense in my head. but then again, i've never really done any extensive audio work.

what do you think? am i wasting my time even thinking about it?

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[maylar 10+ year member]

You cannot parallel another amp with the stock one. You will need to disconnect (or switch) all speaker wires such that only one amp is connected at a time to them.

As for tapping into the sub amp, if it's high impedance and ground referenced you should be able to do that. Look for shielded wire as a clue. If the input wires are not shielded, it's probably a low impedance high level input and not compatible with the RCA preouts.