Well, do it like this if you want to be cool like me.
Results look OEM, with the exception of a little on / off switch.
Sound quality is awesome!!!
Shouldn't take more than a couple hours to install.
Parts: Less than $100.
If anyone in the San Francisco Bay Area wants this, and needs install help hit me up.
Get the parts and come over to my garage in the 925 and I'll install it.
Not gonna go step by step with a write up but heres some basics..
Remove your stereo and install the FM modulator.
Theres a metal bar behind the stereo you can zip tie it to.
Run power wires over to the fuse box, and use the fuse tap to power it.
Take the audio cables and go under the shifter and center console.
With your center console removed, take the power plug out.
Bore the hole a little bigger (i used a uni-bit) so the USB / RCA / 3.5 mm plug thing fits in the hole. plug your USB phone charger into the old power plug, plug in the new USB wire, tape it up and shove it into a hole behind where the parking brake is. Theres perfect space there, but you'll need to extend the old plug wires. Zip tie the remaining wires up nice.
Go back to your car and use the female to female RCA adapters to attach the new RCA wires in your center console to the RCA's coming out from the FM modulator.
Drill a 1/4 hole and install the switch from the modulator where ever you want. I put it behind the parking brake near the lid for the center console
If you did it right you should be able to flip the little switch and your FM modulator will turn on and hijack your antenna input and your Aux will be on. Your radio will need to be on the right frequency for the Aux signal. I set all my presets on FM2 to that frequency. So i just hit FM2 and flip the switch and tada!!!! ...also the USB works to charge my phone too.
Audiovox FM100A FM Modulator with IST2 Isolation Transformer
2 Meter 3ft USB and 2RCA to USB & 3.5mm
Metra 40-SB30 Antenna Adapter for Subaru FM Modulator
Mini Blade Fuse Add-A-Circuit Fuse Holder
a USB phone charger thingy, which you probably already have if you charge your phone in the car.
2 RCA female to female adapters