A3 Subwoofer wireing

[Kjettern]

Hello! I need some help regarding the colors of the sub wires. I already know that:
1 yellow – Right Rear Pre-out
2 purple - Screen
3 green – Left Rear Pre-out
9 white – Remote on
17 yellow/red (speaker out)
18 yellow/brown (speaker out)
19
20 black/white (speaker out)
21 black/blue (speaker out)
22 brown (earth)
23 red/blue (power)

The only question is: What is the 2 purple - Screen cable for? I have a 3 channel amp, so if I wire 1 and 3 to the RCA inputs, and 20,21,22,23 to the speaker outs am I good? Shouldn't the RCA's have some kind of grounding/shielding?

Thanks for answears!