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? What is the best format for the Soundfly to use (NTFS, FAT32, etc.)? How can I access the Fast Forward and Reverse functions using the controls on the unit (without using the remote). Comments 0 comments Please sign in to leave a comment.