Hi Max,
I'm using your app from a couple of years now and, let me say it, I think it's a wonderful piece of coding. I would love to have a custom tag support to sort and organize my music, for example it will be really usefull to sort music from the custom tag "BPM" to create a sense of increasing tempo (or decreasing, who knows the uses). Personally, being a DJ, I rip my vinyls and play them on my smartphone when I'm not home to make a selection of records and this feature would let me choose (for example) only records between 124 and 135 BPM. Unfortunately Poweramp doesn't permit do do such thing and, as I can see, no other player on Android fits this necessity. I think it would be a game changer!
Thank you for your time, happy holidays!