I had the flash drive formatted for FAT32. I don't think the Mazda receiver will recognize Apple format.
To answer your earlier question though, music starts where I left off when turning on the car using an iPod. After the receiver starts up, it's about a 5 second delay before it starts playing where I left off. Music wouldn't restart where I left off with a USB drive. Pretty sure it was just an issue with with folder structure or something. I was using a Sandisk Cruzer 32 GB flash drive. Since I wanted to browse by artist, playlist, and genre, I never bothered troubleshooting and went straight to the iPod.
Good luck in whichever route you choose though!
EDIT: I don't have the Tom-Tom system. I have the basic touchscreen display without the satellite radio. Not sure if that makes or clears up any confusion