two signals into one speaker?

This might be a stupid question but please humor me.

So I want to give my car's stock stereo a little bit of a boost and stumbled onto monsoon amps. obviously I don't wanna spend the money on a new amp and head unit for my car along with all of the wiring for the amp.

I can obtain the amp for next to nothing and it has like 8 channels or so but the problem is that the signals are already split up to be used for a component system (some signals are filtered for a sub and others are filtered for a tweeter). The speakers in my car are just your common speaker in that they just have one set of wires going to them but they are 2 or 3 way speakers. I don't want to cut the wires on the speakers to separate the sub from the tweeter in case I wanna use them elsewhere.
I'm wondering if can just put a sub/tweeter pair of signals together and plug them both into one of my speakers. Thanks for your time.

You can not supply the power from 2 amps at one speaker coil at a time.

If you can access the coils seperately, you could run a seperate wire to them as long as physically this does not conflict.

All in all . . . I wouldnt.

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I know just enough to be dangerous. VERY dangerous.