[lippy]

I wanted something hidden, but something good. What I chose is a JL Audio HD600/4 amp, which has line-level attenuation, so you can plug an iPod or iPhone directly into it. All you see in the car is a cable exiting where the bulkhead meets the floor, and you plug the phone into that cable. I used a grommet and some nice fabric conduit from McMaster-Carr, so it looks clean.

The JL Audio HD amps have a feature where you can control the volume of the amp using an optional pot, so the install will be clean and doesn't require a head unit. I put the pot on a little aluminum bracket I made under the dash, so it is completely hidden but I can reach it easily from the driver's seat. The amp drives 4 JL Audio 5.25" speakers with external crossovers, two in the bulkhead and two in the footboxes. It is far better to use the line-level output on the phone's pin connector, and not the headphone jack, which adds another (very cheap) amp in the chain.

So it works as follows: iPod/iPhone line out (Lightning connector) > Lightning/30-pin adapter > 30-pin to RCA cable > RCA > amp (with line level volume attenuation) > crossovers > speakers.

Let me know if you want more details.