Dude, read your own post (what "Y" is)
LED on means "external routing" or "Separate" as you call it.
lol specs for a controller? no audio goes there.... but sure:
MCU: AT89C2051, 12MHz clock, 5V supply.
buttons need to be held down for at least 100ms to be detected (prevents button spamming)
Action will be taken after button is released.
Output mute at power on: 500ms
Output mutes before power is cut to prevent turn-off transient
I THINK that's about it.