Subwoofer on original sound system?

Hi guys, i'm new to this forum. I just adquired an Skoda Spaceback 1.6, after having a Fiat Punto 1.3 with a JVC radio and with a sound system composed by 1 amplifier one sub and 2 6x9. That radio had 6 RCAs from which I was using 4. 

I don't know if the radio of the Skoda has RCAS, or I'll have to soldate cables. 

Anyways, I found out that under the replacement wheel, there is a battery. So I thought that would make easier the instalation of the amp. I wanted to know if it's possible to install it with the original radio, or I have to change it, or maybe use as a source my old JVC unit.

Thank you.