23 TRD-Sport amp under seat?

I have a GMRS radio installed for offroading. The speaker built into the handset sucks. Instead of mounting a small external speaker like a lot of people do I was thinking of hooking it up to the onboard speakers. After doing some research I think I understand the overall process but I was hoping to get some feedback on if my understanding was correct. If anyone has links to more technical specs and wiring diagrams they are willing to share that would be greatly appreciated.

The GMRS radio has line level output. I have a 2023 TRD Sport with the base system. It looks like the amplifier is underneath the driver seat. At work right now but I will confirm this when I get home. If I use a small mixer to join the two audio streams then that would allow the GMRS radio to share the speakers while still using the infotainment center and get the output to speaker level input.

Does the input to the amplifier have 1 wire bundle or is it individual inputs per speaker? If the input is a harness that just joins the individual wires to 1 plug could I cut and splice one of the wires from the mixer output? Am I missing anything?

Not looking to cut out the sound from the head unit when the GMRS radio is going. Not looking for an A/B switch. I also would prefer not to use the aux in since I would like to have my music and infotainment center to still play.

 

The Tacoma have two options:
if you don’t have the JBL system, the six speakers are powered by the head unit itself. No external amp.
If you do have the JBL system, the amp is back behind the seat by the subwoofer it receives a digital signal from the head unit So there is not really any way to interface with it aside from replacing the head unit.

Could you get that audio signal integrated into the factory speakers? Yes. Would you spend a ton of money to do it? Also yes. Is it all worth it? Probably not.