I haven't read the whole thread so please forgive me if I am barking up the wrong tree.
Proteus family 2.2 sysex page 6 for parameter
F0 18 0F dd = header
55 01 02 = Parameter value edit
02 07 = parameter number = Layer select
00 00 = value (Layer 1) (-1 = all layers )
F7
F0 18 0F dd 55 01 02 02 07 00 00 F7 = Select layer (pp53)
F0 18 0F dd 55 01 02 02 0B 20 7F F7 = layer volume value -96 (pp 59)
To unmute it you need to remember the value before you turned it off.
You can get most of this stuff from Prodautum.
Jan use to have his output sysex displayed, but I can't see it in the last version.
Instead use MidiOx and loopMidi to see what he is outputting when you click a button.
All the best
Royce