"Accessories that use only Bluetooth Low Energy (BTLE) (note: BTLE-enabled HomeKit accessories and BTLE-enabled MFi Hearing Aids are part of the MFi Program)"

(MFi = made for iPhone) https://mfi.apple.com/MFiWeb/getFAQ.action#1-2 https://developer.apple.com/bluetooth/

Have fun with MIDI quality. The only way BTLE is sending mp3 or higher quality is through the MFi Hearing aid protocol Apple owns and keeps under wraps.