Could there please be more preset checkboxes when expanded? Maybe an ‘add’ button to increase according to your own wish. I’d like to pin around 10 sample folders, tho 8 would be an improvement 
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Instead of 4 preset boxes located horizontally at the top, they could be lined up vertically beneath the last search criteria (themes), so you could also write a short description next to it, like: drums, bass, vocals, perc, string, fx etc.
cheers,
rico