Midi Controller changes - Boss related

[Darug]

So, I've been using BH for a few years now, and great overall.
I play Synth, Guitar + Guitar Synth.

One of the things I would like to do is, to be able to mute an instrument at startup, given my guitar is playing either thto the Boss GX100 Guitar Processor , or the Boss GM800 Guitar Synth (or sometimes both).
I was looking at exploiting the ability of sending a control change, so 1 volume will be muted (I assume 0), and the other a value of @100-127.

I looked (IE https://nickfever.com/music/midi-cc-list),  and from what I have found so far the General Controller value (for volume) is 7, therfore next value should be 0? However, upon my testing, I still have volume, therefore unsuccessful. Any clues/hints?   

[Darug]

Otherwise, do I have to look at Hex Code? I've not really played with Hex code much, but tried the following value, but no luck there either

B3 07 00 (Based on the following:-
 
IE (-)Volume (Controller number 7)
Status  2nd Byte 3rd Byte
BnH     07H      vvH
n = MIDI channel number: 0H - FH (ch.1 - ch.16)
vv = Volume : 00H - 7FH (0 - 127)

No success either.
Device is on Midi Ch 3

[arlo]

You don't need to use the Raw MIDI field to send control change messages. You can set the channel on the MIDI Device page and then enter the controller number (7) and value (0) on the MIDI Preset page.

But you do need to consult the documentation for the device you want to send messages to. The link you're referencing is for the MIDI specification, but most devices only implement parts of that, or implement the same functions in non-standard ways. In other words, it's possible that your devices don't support a volume control change, or they've implemented it with a different MIDI messages. If you can't find what you're looking for in the user manual, you can contact the manufacturer and ask, "What MIDI message can I send to change the volume."

Some devices also require changing one or more settings to enable MIDI input.