I hope that I have researched enough posts to quantify this as a new idea. Could one not eliminate the dash tweeter and bridge the crossover/amp to use a regular 4 ohm speaker in the front door? Take the neg. output going to the tweeter (from the bundle that plugs into the amp/crossover thing) and wire it to the negative input of the new door speaker. Take the pos. output going to the tweeter and splice it to the neg. output going to the door speaker (blk.wire that was connected to the door speaker). This would work fine on most amps, but not sure how the built-in crossover would effect things. Unless someone tells me that it would never work, I don't mind trying it. I plan to get rid of the factory deck and amp/crossover thing anyway.
I did gather this info from here----
Tweeter neg. out = yellow/Black(left) Orange/red(right) Pin #2 (cut wire and connect to new speaker neg. in)
Tweeter pos. out = yellow/red (left) tan/black (right) Pin #7 (splice together with door speaker neg. out)

"Bridging" it taking a stereo amplifier and making it single channel.... and you can use a 4 ohm speaker with a loss of 3dB of output.... +/- 3dB in the minimum output change the human ear can detect with music.

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The tweeter and woofer are run in series to make 4 ohms that is run off of one channel of the amp. The other channel feeds the rear door woofer. Two total amps, one on each front door. The amp is designed to run a 4 ohm load, just not with a 2ohm tweeter and 4 ohm aftermarket speaker in series like they were before. Eliminate the tweeter and step back to 4 ohms. Assuming that the tiny amp in the door isn't a 3 channel. The wiring idea seems like bridging, but I think I'm just eliminating the tweeter. The problem is the signal run through the crossover that will be put back together. It's the high and the low signal output put back in series together. Probably won't sound good but this place is full of half-baked ideas.
I also checked the impedance of the Infinity speaker that came out of the door. 2.6 ohms, not 2, which means that a 4 ohm speaker won't overwork it as much as thought. I am running a 4 ohm speaker in place of the Infinity now and haven't lost too much power. Sounds good. Maybe I'll get more power back by trying the wiring idea.