I was thinking if this could be possible before lol
A quick explanation after a google search!!

The AMZUSB001 allows connection of a mass storage USB device to an original equipment Mazda head unit. The interface offers MP3 folder and track control along with USB power to the device. The kit includes an additional 3.5mm input and SD/MMC card reader.
The AMZUSB001 fits Mazda branded radios found in the 2/3/5/6/MX-5/RX-8/Tribute from 2000 onwards with a 16 pin CD changer connection (2 rows of

Please note: interface connects to reverse of radio
http://www.incarexpress.co.uk/view_product.php?partno=CTAMZUSB001