As far as running the speakers off of an external amp, it's quite a bit of work and much more expensive than people originally think. You have to run power from the battery to the amp (4ga wire w/ fuse), you have to run RCA cables from the headunit back to the amp to get the sound signal to the amp (these can cost A LOT depending on how long they need to be and how well they are shielded from noise interference) and then finally you have to run the actual speaker wire to each of the 4 door speakers.
I used to do LOTS of audio work when I was in the import scene 6 or so years ago so I could do this to a Honda in 1.5-2 hours max starting from scratch but have never tried to pull wires thru my Libby.
Let me know if you do decide to do this as I'm curious just how involved it would be
