Quote Originally Posted by MLA View Post
In a perfect world, we want to tune using the weakest source, which is typically BT or old school AUX headphone jack. The downside is, now stronger modes like USB and Tuner can now over drive the system if the user is not careful. If we tune so max volume is, say, at 95% of head unit volume when using BT, then if switched over to USB, now max volume before distortion, may be like 65% of head unit volume.
It's funny, my Supra is the opposite. Bluetooth from my Android is a far louder signal than USB from my wife's iPhone.