I started thinking about this. I think I like the seperate BT better. IF you are still using a HU. This way you can go.. BT->HU->420->Amps
You would need to reset your gain I would think going just BT->420>Amps? You also lose the ability to use the transom remote (mainly used for just mute since the HU stays at 28 all the time and volume controlled with 420)..
Great if you want to completely ditch the HU I would think..