What is the best way to store MP3 on the the SD card / USB Stick to get the maximum number of tracks? If i was to save each CD in its own folder am i right in thinking i could only have 99 CD's on each SD card or USB stick? John July 02, 2018 23:53 Updated Follow The Soundfly AUX can only support up to 1999 WMA/MP3 files and 99 folders up to 5 levels depth. Related articles Instruction Guide Does it support and transmit in stereo from USB, SD card and aux in? Does it have any sound equalizer settings or option? Comments 0 comments Please sign in to leave a comment.