No hissing/crackling trouble on my side. Regarding the filecount limit, it's related to the library and the fact that it automatically rescan your microSD each time you power on the device. So, up to 3000 audio files, the scan is lightning fast (routine is ASM optimised), but over this 3000 files limit, the scanning takes up to 20 minutes to complete (tested with a 512GB microSD containing around 30.000 files). Yes, their database scheme and arbitrary files limit is absurd, don't ask me why this was implemented this way, it's just like that. As you have noted, the hardware is top-notch, indeed and the device delivers plenty of listening pleasure. As for the firmware version, it's actually stuck at 8.1, that's it. It's a customized version of the very first iterations of the "Hiby OS", looks alike the "Hifi Walker H2" OS, kind of. It's okay. Bluetooth works fine, USB DAC mode works fine too. There's a 9.2 version for the firmware, but that's not for the "F.AUDIO FA4", that's for a rebrand of this exact same device under "LIMETECC" label for the asiatic market. I've tried this firmware version (9.2) onto the F.AUDIO FA4 and the display is inverted : upside-down with video inversion. This was done on purpose to prevent users of the F.AUDIO FA4 model to upgrade their device's firmware. You could use it, but everything is inverted, so right is left and vice-versa, you have to lower the volume to crank it up, etc... I've personnaly rolled back to the previous version (8.1). Otherwise, one way to bypass this stupid 3000 files limit is by using ISO files or FLAC Full albums with cuesheets. Also, I ended up with 450 (60GB) ambient mixes produced by
Low Light Mixes wich is roughly 450 hours of music. That's plenty. Else, i just connect to my LG G5 bluetooth and feed audio to the FA4 this way. So, it works great as a bluetooth amp too !