TotalMix FX, Options, ARC and Key Command Settings. Further TM FX hotkeys are described in the manual.

Did you miss chapter 25.9, Hotkeys and Usage? There are some more hotkeys in there.

BTW, I wish you good luck for going back to China soon. I was separated from my family since March and am currently in local quarantine in Bangkok. Hope to see them soon. These are crazy times for most of us.

TotallMix shortcuts only works when its window is in focus.

Use Keyboard Maestro to send the MIDI to TotalMix with your desired shortcuts. That way you can control TotalMix even it's in background.

Set "Keyboard Maestro" as input ports in Option -> setting -> MIDI, and send note-off signal on note 54-61 for snapshot 1-8.

On Mac - You can also do this...

I prefer this method, as it doesn't need to have any 3rd party software installed/or any additional services/apps running.

1) Save your Snapshots to your default config dir via "File - Save Snapshot as..."

2) give your snapshots a proper naming - like this f.ex:
1_Snap.tmss
2_Snap.tmss
3_Snap.tmss
...

3) Open the (Siri-)Shortcuts App and create a new one
4) On the right side from Apps Section, drag "execute Applescript" snippet into main Section
5) Paste the following code into the Applescript Code Editor (opens the snapshot file beginning with "1")

#if TM App is not opened, open it
tell application "Totalmix" to run
try
    tell application "System Events"

        # Bring Totalmix App to the front
        tell process "TotalMix FX"          
            set frontmost to true
        end tell
        
        # Open the "Load Snapshot..." Window via Hotkey (Command+O) in my case
        # key code 31 = "O" on Keyboard
        key code 31 using command down
        
        # wait for Open Dialog window 1 second
        delay 1
        
        # Press 1 on Keyboard (18 = "1") - selects the first file which name begins with 1 - (1_Snap.tmss) in this example
        key code 18

        # Press Return (36 = "Return") on Keyboard - the OK Button in the Dialogue Window
        key code 36

    end tell

# some basic Error handling
on error errMsg
    display dialog "Error: " & errMsg
end try

6) click on the top right "i"-icon and check that "Use as fast action" and "Menu Services" is enabled

7) Push the Button "assign a Keyboard Hotkey" and enter your preferred Key-Combination to it

7) On first launch, you should get a message if your Shortcut is allowed to execute Applescript

8) Save it and it and should work. Even if the Shortcut App is closed, your custom Hotkey triggers always the script. Doesn't matter if Totalmix is not in focus or minimized. 

You can check this in Mac-Systemprefs -> Keyboard -> Keyboard-Hotkeys -> Services -> Hotkeys

Yes, this is an amazing piece of software.