The dirty USB port makes sense because the sub worked via bluetooth and not AA, I would think any audio setting would apply to both bluetooth and AA interfaces and the sub did work with my phone via AA. I'll report back, thanks.
Android Auto works with a USB port, I chatted with Crutchfield support, they suspect his phone could be set to mono, I'll check that when he gets home. It worked fine with my phone.
I plugged my phone in to see what would happen and everything seemed to work with my phone (S10e). I was using Pandora and he was using Spotify. The head unit is a Alpine ILX-407.
My son has a Samsung A50, when he connects to his android auto via a cable, the sub stops working, however it works fine when using bluetooth. Any ideas?