I recently upgraded the audio on a new JP premium using the info on this thread which made things really easy. I created my own CN5 connector and 3D printed the speaker brackets for the backbox. I'm powering the amp from the service port since I use smart plugs to power my games.

Here's what I used for reference:

Amp (Fosi Audio BT30D): https://www.amazon.com/dp/B07K7NJ4QN

Backbox speakers (PYLE PL53BL Blue Label): https://www.amazon.com/dp/B005FNFIS6

Cabinet Sub (Pyle PLPW8D): https://www.amazon.com/dp/B007JV7F4W

Huge improvement over stock.

Since my pins are all powered through smart plugs (https://www.amazon.com/dp/B091FXLMS8) I just plug the amp's DC power supply into the service outlet.

Has anyone had issues with the Fosi BT30a amps? I've got 1 that is perfect, 1 that is a little noisy, and 1 that is really noisy. I've swapped amps between games to rule out any cabling and power supply issues and the noise follows the amp. I've got the worst of the amps apart now to test it, but I wanted to check if anyone had seen this too and figured anything out.

I replaced one of the bad Fosi BT30D's with one of these DIY TPA3116 chip amps and so far so good. I'm still using the Fosi power supply.
https://www.amazon.com/dp/B089KT3FG9

No idea yet what is going on with the 2 noisy Fosi BT30D amps. I ordered them at the same time, so maybe these 2 are a different design rev from the first one I bought a few months back. Or they started using some lower quality parts.

A downside to be aware of with the TPA3116D2 based amps is the unsecured bluetooth which takes priority over the line input. Anybody with a phone within range can connect to it, and I've had the sound drop a couple times mid game because of that. And if you want to stream music over your pinball speakers it can be confusing when you have several of these amps because they all have the same name.