4 channel amp wiring on premium sound system

[nathk24]

I've had my cl9 for little over a month now and it has nav and pss fitted. Whilst its not bad for a factory sound system i find it lacking some what as i fitted a full system in my last few cars.Dont want to mad nut I'm looking at a 4 channel amp to power new front components and new 6x9's in the rear shelf and leaving the rear doors running off of the factory amp. Amp i'm looking at has high level inputs which i have never dealt with before as ive always used a different head unit with rca's. Does the signal for the fronts need to be taken before the factory amp or after?

 

[nick 9-5]

Personally I'd say before as you're amping the signal with the 'new' amplifier. I'm running an amp with HLI but only running a sub, so have split the signal from the rear speaker wires. I've got the povvo spec system so no amplifier.