Here's the code I'm using for the midi callbacks. The basic problem to address is that speakerB and Dim are both toggles; you just send 1.0, and they switch their value. But the mutes are on/off, so you have to store the information about the current mute status in a variable somewhere. I keep it in the oscin node, because they could have been muted by the GUI or the hardware controls.

The lookup tables are to map from note numbers and controller numbers to the OSC messages I want them to send.

# me - this DAT
#
# dat - the DAT that received the event
# rowIndex - the row number that was added
# message - a readable description of the event
# channel - the numeric value of the event channel
# index - the numeric value of the event index
# value - the numeric value of the event value
# input - true when the event was received
# bytes - a byte array of the received event
#
# Example:
# message  channel index value     bytes
# Note On  1        63   127       90 2f 127

mutefetch = op('/project1/oscin2').fetch
sendchan = op('oscout1').sendOSC

def normalize(inv, max):
    return (inv / max)

# Control -> toggle mappings.   
cclut = {
    105: '/1/mainDim',
    106: '/1/mainSpeakerB',
}

def handleCC(index, value):
    v = [normalize(value, 127)]
    toggle = cclut.get(index, False)
    # Toggle buttons; send on push.
    if toggle and value == 127:
        sendchan(toggle, [1.0])
    # main fader
    if index == 8:
        sendchan('/1/mastervolume', v)
    # 8 pots
    if index >= 22 and index <= 29:
        addr = "/1/volume{}".format(index-21)
        sendchan(addr, v)
    return

# kOSCScaleOnOff; requires looking up the current state
# to make the button reverse it.
# For reads, we strip the leading /; for sends we keep it.
tlut = {
    41: '/1/mute/1/1',
    42: '/1/mute/1/2',
    43: '/1/mute/1/3',
    44: '/1/mute/1/4',
    49: '/1/mute/1/5',
    50: '/1/mute/1/6',
    51: '/1/mute/1/7',
    52: '/1/mute/1/8',
}

# kOSCScaleToggle; sending "1.0" causes it to happen.
plut = {
    46: '/1/busInput',
    47: '/1/busPlayback',
    48: '/1/busOutput',
}

def handleNote(index):
    # The toggles; send blind.
    if plut.get(index, False):
        sendchan(plut[index], [1.0])
    # The stateful ones; read, then send the opposite.
    if tlut.get(index, False):
        # Get the mute represented by this pad
        chan = tlut[index]
        # Grab the status of it from the OSC DAT
        # Specify a default, because if the channel is disabled or doesn't
        # exist, we don't want an error here.
        curr = float(mutefetch('m' + chan[-1], 0))
        # Got a 1? send 0. Got a 0? send 1.
        sendchan(chan, [1.0 - curr])

       
def onReceiveMIDI(dat, rowIndex, message, channel, index, value, input, bytes):
    if (message == "Control Change"):
        handleCC(index, value)
    if (message == "Note Off" and channel == 10):
        handleNote(index)
    return

And that's basically it. I added an executeDAT to run some commands at startup (to select the playback bus) and exit (to turn all the lights off - the keyboard lights stay on when I turn my PC off, so it's annoying otherwise).

The other things to do if you're new to TD like I was:
1) You have to add the midi devices via the midi device mapper
2) You have to toggle whether it should be responsive while minimized; otherwise these controls all work while the window is up, but not when you minimize it.

I hope this is useful to someone else! My next steps are probably to add in some snapshot navigation via other buttons. The other nice thing about this setup is that you can map multiple OSC messages into a single button press for some automation of things.

My main sadness with this is that the keyboard doesn't have motorized faders, so when you start moving a dial the mix will instantly snap to where your dial is, instead of waiting for you to crossover the current setting. That can probably be fixed with some more variable storage in the OSC dat, but I'm not there yet. :-)

nice work... i don't understand code too well but the functionality looks good.. do you know if Touch Designer would be able to connect Totalmix with Reaper via OSC ? i have been looking for a way to get Reapers faders to control Totalmix faders (and vice versa) and mutes also..  Totalmix OSC responds to 1/Volume1 and Reaper OSC responds to n/track/1/volume, so from what i can tell i just need some software that can patch those OSC patterns..

awesome.. looks like cool software, i'm downloading it now.. hopefully I can work it out..