TP1 - battery +

TP2 - battery +

TP3 - GND

TP4 - battery +

TP16 - momentary battery +

TP20 - pulse GND if back, left, TV input, *

TP21 - pulse GND if MIC, select, -, power

TP22 - pulse GND if home, right, +, i

TP23 - pulse GND if down, up, mute

TP27 - battery+/pulse GND if up, *, i, -

TP28 - battery+/pulse GND if back, MIC, home

TP31 - battery+/pulse GND if left, right, select, down

TP32 - battery+/pulse GND if TV input, power, +, mute

TP35 - 3.3V  This turns on as soon as a button is pressed but stays on for several seconds after the button is released.

TP20, 21, 22, 23 are always battery+

TP27, 28, 31, 32 are battery+ & pulse GND only when their group is pressed

GND pulses are 30us long, repeating every 25ms

Power & MIC suck 40mA.  The rest suck 20 - 30mA.  The existing brain can stay around just to manage power & backlighting.  It blinks error codes & sucks amps but back lighting looks better than nothing.

Q1 is a P transistor which feeds the LED battery +.

Q5 lights a blue LED when the mic button is pressed.

Q4 lights a green LED when any other button is pressed.

Q2 flashes a red LED to signify an error after every button press.  That could be disconnected.

11 signals in total would be required.  The buttons require 8 signals.  Then there's 3.3V, GND, & LED.

There's room for a 27x24x5mm board.  A bunch of standoffs press the board against the buttons.  Former space for the speaker can be used for excess wire.