What is the difference between the regular one and the one with RCA outputs?
http://www.crutchfield.com/S-XP7CV1q...7550&s=0&cc=01
vs
http://www.installer-parts.com/by_item.php?it=70-7551

which would be best if I'm just adding a head unit now but might change speakers/amp at a later time?

 

Do you have the Bose system?

 

The one with RCA's allows you to hook up your aftermarket H/U to the Bose Amplifier using RCA's. You could do this with the other one as well, but you would have to make your own RCA connector. I would get the one with RCA's if you are getting a high quality H/U that has at least a 4V pre out voltage. Once you replace the amplifier, you probably won't need the speaker outputs behind the dash.

 

The OEM Bose HU signal to the Bose amp is about 2 volts, so you may have to be careful with the volume level of your HU since you can't adjust the gain on the Bose amp is you send speaker level signals to the Bose amp. You may need a LOC.

 

sorry, yes i do have the Bose. I'm getting the kenwood ddx8019 which has 5v pre out voltage. So what I am understanding is that I should get the harness with the RCA cables if I plan to possibly later on remove the Bose amp and replace speakers?

 

Also, I plan on putting this in for now
http://www.crutchfield.com/S-XP7CV1q...SLC4&s=0&cc=01
still compatible?

 

You don't need the harness with the RCA plugs. Your Kenwood has 3 sets of RCA outs already. I think you will need some interface like the PAC OEM-1 to go between the Kenwood and the Bose amp, or you may be able to use the Kenwood's RCA outs and connect them to the Bose amp at the wiring harness. I've never done the aftermarket HU to Bose connection, so maybe someone that has done it can help.