Some aftermarket amp/ head unit ??

[ComongooseTSX]

Hi all, I just bought a 2004 TSX this last week for a cheap $6k. Anyways I was quite disappointed to find that the head unit is integrated into the hvac unit and vents. Anyways I was figuring I would just run all my alpine speakers and amps through the stock head unit. Now I saw a lot of recommendations on using an LOC, since there are no pre-outs on the stock HU. Now my buddy hooked up his sub just splicing the speaker wires into RCA connectors. I had no idea the voltage was higher out the speaker wire, but on his amp it seemed to work. Will there be a sound difference running it this way versus through an LOC? Also I was considering installing an aftermarket head unit. I have a pioneer I bought 6 months ago which came with 3 4V pre-outs. How will the sound compare to just running the stock speaker wire from stock HU to LOC to amp versus the pre-outs from the pioneer HU I bought? One more thing, Can I run and aftermarket HU and have it manage power to everything like you normally would when replacing a HU, as well as have the stock HU be the master volume control for the HU? Thanks in advance for any advice or answers. BTW i have not seen to many custom HU install pictures.

[ComongooseTSX]

anybody?