Adding aftermarket subwoofer amplifier to JBL amp sub output

I have a 2019 TRD Pro with the JBL Entune 2.0 radio. I can live with most of the common issues it gives me, and I like the stock look, volume and tuning knobs, and use the CD player often (so no replacing the head unit) but I'd like to do my own subs behind the backseat as part of a mild audio system upgrade and attach some sort of signal cable to the sub output on the amp. If it's as simple as clipping the ends of the wires and putting RCA connectors on the ends, I'd certainly do that, I have done several complete audio systems on older vehicles with aftermarket head units, but this will be my first time opening up a premium audio system in a newer vehicle, and I'd rather not get into it and then have it not work. Additionally, I have seen all the plug and play sub upgrades for sale, and have decided that won't work for me. I'm pretty particular about the car audio equipment that I use. Any advice is much appreciated.

 

you've got the right idea.

you'll need to use the stock jbl amps sub output as the input to the new amp, but it will be connected as a speaker level signal to the new amp, instead.

typically, rca connectors on many amps are low level signals, meant for connecting different aftermarket gear together. but many newer aftermarket amps now accept both high or low level signals on their rca connectors-- it really just depends on which amp you select for the task.