Wiring Sub/Amp to standard head unit

Evening ladies and gents.

So, currently iv just recently bought a sub/amp and wiring kit which I am going to have wired professionally however have been advised that the head unit that come with the car does not have rca to wire up to.

I have a Fabia Monte Carlo 2011 Tech with the Amunsden Sat Nav head unit.

Im seeking information on how or if people have succesfully wired subs up and how they done it or if they know of any rca adaptors?

- Tony