Interesting study. I might have to try out ripping my CDs into 320kb/s MP3s just to try it out. I will say, that the difference between CD sound quality vs Bluetooth streaming was a lot more noticeable in my Speed3 than in the CX-5. I guess that means the CX-5 has a better sound system for streaming music.
I think bluetooth streaming might reduce the quality so that might be part of it too. Not sure bluetooth could handle that bandwidth. Connecting music source directly to the car might make a difference.