We have an '04 Accord V6 coupe with the factory 6-disc CD player. What is the cheapest, easiest way to add an aux-in to the factory unit?

Also does the factory unit have any pre-amp outs to feed an amp, or should I use the rear speakers as a signal?

 

Usually the factory radios don't have pre-amp outs, you're just gonna have to pull the head unit to be sure.

The easiest way to add aux-in is the iPod/MP3 interface: http://www.handa-accessories.com/accelect03.html

You may find it cheaper on eBay or local craigslist.