After further testing this is what I found. I took the same song ripped from the original CD to an MP3 and tested all the inputs.
Original CD - Obviously excellent quality and volume
MP3 on a data CD - excellent quality and volume
MP3 on SD – lower quality and volume compared to original
MP3 on USB - lower quality and volume compared to original
I had another person swap from the original CD and MP3 CD without me knowing which was which and I could not tell the difference. This shows that the AVIC has the ability to play MP3s very well. I just don’t understand why they seem l