Hello... there are 16 midi channels, set any Hardware input/output midi a channel #... Master (Roland?) would be where you Store/Playback your Midi information... Slave would be a device that plays back your MIDI information.
When recording MIDI data, your Roland can be in OMNI mode, to read all incoming channels and MIDI data, and you can then send that MIDI data to Abletron thru USB?
Master and Slave setting are used for PLAYBACK... and the Master, is the MIDI Transmitter and the Slave, is the MIDI recievers/Players of Audio Data.
When in Playback, you can have Audio from your (Slave) tractor outputs, and requires a input midi cable and channel setting...
When in Playback, you can have Audio from your (Slave) KORG outputs, and requires a input midi cable and channel setting...
When in Playback, you could have all your MIDI Audio from the ( master) Roland outputs...
Playback Audio options can very with your setup... as each unit has it's own audio output... and can read/play Input/MIDI data.
But RECORDING the MIDI data, use the Roland MIDI inputs with the Korg as midi output channel 1 and tractor as midi output channel 2 and start with your Roland in Omni input/mode first, too see the korg and tractor talking to it.
Set the abletron MIDI Track inputs to Omni mode first to verify your midi output devices are communicating with it... and sort out your connection choices and then set up a Individual MIDI Track input for each device, by setting the MIDI channel for each Hardware device, to only record that Channel ( device ) DATA.
When Playback, you could have all your MIDI Audio from the ( master) Abletron Tracks ( thru USB ) and your roland/tractor/korg will be your Playback/Slaves.
You need to first determine your Recording connection needs... will there be one player to record or 3? and where will you store the DATA... And how does it get there?
You need to determine your Playback connection needs... do you need live instruments? and Midi playback? what Audio outs do you want to use? Where do you want to Plug your headphones in, When editing your Midi Data? Where do you want the Audio signals to go when your Playing back for other people?
MIDI is very versitile and your Audio devices are too... there are many setup/record/playback options here.
MIDI outs go to MIDI ins... MIDI ins go to MIDI outs.