ciubaka Thanks for the insight! That makes sense now. I noticed that with the stock system hooked back up, unplugging that blue USB causes all audio to stop just like unplugging the C240B plug that holds the amp power line.
I tried to use an adapter (female mini USB to USB-C) to connect it to the DUDU7s USB-C port but no luck. I'm assuming that port is only for USB input and won't send signal to the amp. So disappointed, I actually really like the DUDU7 much much better than the SYNC ststem.
I've decided to keep it still and just get an amp to bypass the SONY one. Just a heads up if you're planning to do the same...the stock speakers are 2ohm so you'll need a 4channal amp that is 2ohm stable. Otherwise you have to replace the speakers too which is likely what I'm going to do. Cheers!