jhorologySorry, but I don't understand your questions. Could you better explain what you are getting at?
edit: I missunderstood your 'macos' for 'macros' instead of "MacOS". I have no idea if it works in the boot options of MacOS. However, it works like a normal keyboard, so I don't expect anything special. For the USB MIDI, I don't know if you want this device to play midi sounds or if you want it to act like a piano to your computer. In both cases you will probably have to write software yourself.
PawnerdSorry for typo, yes it means MacOS startup key combination.
http://support.apple.com/en-us/HT201255
I tried some other kits with qmk_firmware, they all didn't work.
This is a must-have feature for buying this keyboard.
jhorologyI'm not sure if any particular configuration is required for the boot settings to work - they had luck here by trying different ports: https://apple.stackexchange.com/questions/87349/how-do-i-get-into-boot-options-with-a-non-mac-keyboard - if other external keyboards work, I would imagine any keyboard running QMK would work :)
QMK supports USB-Midi :) you can assign keys to CC and other midi actions! I don't think it's heavily documented right now.