The .7z (7-Zip) format is used for this firmware because it provides significantly better compression than standard ZIP, making the firmware image smaller for distribution. Other Potential Interpretations
In this context, (specifically the file DX90FirmwareV2.1.5-L5.7z ) represents a specific iteration of custom firmware with the following characteristics: Base Version: It is built upon the stock version 2.1.5.
high-resolution digital audio player, developed by a user known as Lurker00. iBasso DX90 "L5" Firmware