(NON-JBL) Bypass Factory Amplifier for more RMS?

Tried searching for an answer but all threads return JBL results, I don't have the JBL system.

I do have an aftermarket headunit (KD-R895BTS) which advertises 22w RMS and best result I can find is the factory amp outputs 12w RMS.

Would negating the factory amplifier drive my speakers I have coming (Rockford Fosgate T1675-S) better?

If so how do I do that?

Best place to mount the crossovers for the tweeters where they'll be most protected from potential water intrusion?

 

If you don’t have the JBL system, you don’t have a factory amp

In the non JBL system, the radio powers the speakers.
Take out the radio and replace it, now the new radio powers the speakers

 

From what I see with minimal searching is that your radio has 3 sets of RCA outputs. Sub, left, and right. Use these to feed an external amp. If you don't want huge amounts of power, you can use the factory wiring for the speakers. Disconnect them from the radio harness and connect them to the amp outputs.

I believe Alpine makes a 4 channel amp that fits in the dash. That would make life very easy having to only run one wire from the battery to feed the amplifier.