
Hey, there is no point converting from Mp3 to flac as Mp3 files are already in a degraded formats ...(that is how the software is a able to reduce the size of the audio files).
Flac is one of the higher formats (well supported in the open source community...), there are even DSD/DXD HD flac types...
So once the files are in Mp3, the quality is lost due to the algorithm so going back (from XXKbps MP3) to a higher quality like flac or other higher formats ... is a waste of time. Hope that makes sense. Once the files are in Mp3 it is already in one of the lowest audio formats (256, 128, 64, 32... Kbps MP3).
Sorry i can't help you with the webGui remote as i use a different WebGui/App (Pro X100).