Concerning the Pioneer vsx-1019ah-k that I originally mentioned, I went to the Pioneer site and looked at the manual in pdf format. It says it has a USB port for digital audio players (MP3 players) of format FAT16/32.

Here's a link for it. Just click on the Documents tab, then the "owners manual" link. I then searched for MP3 and it came up with just a few lines in the document.