The golf head units don't come with RCA's
You can purchase PnP sound system direct and install your self however you will have to take the car to VW to have the correct DSP settings loaded onto the PnP sound system.
When I was looking into install one none of the dealers I contacted had the correct tool to do this and weren't interested in purchasing the tool for a once off job.
You used to be able to get the PnP system with the correct DSP setting preloaded but they are no longer available.They all come preloaded for a Polo 6R.
I ended up going for a Match PP52DSP and Match PP7S-D made by Audiotech Fischer.
They make the VW PnP system so it is essentially the same sub,amp and DSP.
The big difference is the PP52DSP you can program the DSP yourself by either downloading the setting from their website or by programming your own setting using a laptop and some sound testing equipment.I personally just downloaded the settings.The other difference is you can move the system different brand of car and just program it for that particular car.the PP52DSP also has RCA output's on it so you can add more bigger sound and still benefit of the use of a full DSP.