I don't see how USB to AUX will work.
USB i digital. AUX is an analog singnal. You could blow up the device or your mobile or both!
A better option is to look for one of these Multi functional FM transmitter cum BT Cum everything-
Wireless Car FM Radio Transmitter Audio USB SD Card Slot Kit MP3 Player + Remote | eBay
Bluetooth car charger-Hands Free-Car MP3 Player-FM Transmitter-Dual USB Charger | eBay
CARG7 LCD Bluetooth Car Charger FM Kit MP3 Transmitter USB Handsfree Mobile | eBay
USB i digital. AUX is an analog singnal. You could blow up the device or your mobile or both!
A better option is to look for one of these Multi functional FM transmitter cum BT Cum everything-
Wireless Car FM Radio Transmitter Audio USB SD Card Slot Kit MP3 Player + Remote | eBay
Bluetooth car charger-Hands Free-Car MP3 Player-FM Transmitter-Dual USB Charger | eBay
CARG7 LCD Bluetooth Car Charger FM Kit MP3 Transmitter USB Handsfree Mobile | eBay
all those options have 1 imp thing (atleast for me) missing, android auto!!