About to be doing an install in a newer charger and  a dash kit for an after market radio is like $500 so just tring to see what the best option would be if the customer is not trying to spend 500 on just a dash kit . .  Just going to be adding a sub and amp

I'm in a similar situation so I'm looking to gain some knowledge from whoever else chimes in.  

They seem to be the best alternative and range in quality and price.  I noticed there are a lot for cheap, but have come across some more sophisticated ones.  My understanding is that you tap into factory speaker wires with the converter in order to setup the rcas.

I have my eyes on this one at the moment:

http://www.sonicelectronix.com/item_43567_AudioControl-LC2i-Ships-as-New-Black-Version.html

It may be overkill for a simple sub/amp install so I'm interested to hear what other people have to say. 

For just adding just a subwoofer and an amplifier for it, I wouldn't be to concerned with spending a lot of money on a line out converter. The above linked AudioControl unit is a good option and about at the top of the price range for line output converters. If you are planning on adding a full system I would look at more of a digital signal processor like and miniDSP or PPI DSP-88R  

Personally I would use the Rockford Fosgate RFPEQ since it has both high level inputs and functions as a line driver giving you more headroom if your signal isn't very great.

 

http://www.sonicelectronix.com/item_94272_Rockford-Fosgate-Universal-Punch-EQ-RFPEQU.html

First thing I would do is verify that the outputs are doctored.  I've seen quite a few American cars where all the processing occurs after the headunit and therefore just splitting the wires is enough.

6 hours ago, Julian said:

Personally I would use the Rockford Fosgate RFPEQ since it has both high level inputs and functions as a line driver giving you more headroom if your signal isn't very great.

 

http://www.sonicelectronix.com/item_94272_Rockford-Fosgate-Universal-Punch-EQ-RFPEQU.html

Is this one a good option for just a sub & amp setup?  Is tapping into the rear speakers good enough?

I'm in the same boat I have never not changed my head unit until now my cruze has such a nice nav unit I don't want to take it out some I'm gonna be ordering a audio control line out driver plus eq for mine. To bad I'm not using my JL HD 1200 it has speaker level inputs already built in. 

Beware speaker level inputs in modern cars.  Can be horribly processed.  I would measure the output across the frequency range I was going to use first.

18 hours ago, mbarber25 said:

Is this one a good option for just a sub & amp setup?  Is tapping into the rear speakers good enough?

In most cases its just fine, with the RF you'll have a bass boost which should help if your stock HU is horribly processed.