Noob Bloos...

[Lizard of Oz]

The most obvious thing first, you need make a connection between a USB port on you computer and the PC port of the MRCC so that the MRCC is available as a MIDI interface in Live. See Live's MIDI Ports for more info.

What you need to do is connect USB controllers to the HOST ports on the MRCC, connect synths to the MIDI DIN ports, and then create routes from HOST to PC and from PC to DIN MIDI. Here's more details:


To use your USB-controllers with Ableton Live

1. Connect your USB controllers to the 4 USB HOST ports  on the MRCC
   
2. In the MRCC, create a route for USB-INPUT to one of the 12 OUTPUTS of the PC port (see pg. 13 in the MRCC manual). Use a separate output for each controller, then it's less confusing to configure the ports in live.
   
3. Set up the controllers in Live (see Using MIDI controllers with Live), note that the Midi Ports for your controllers are those of the MRCC!
   

To control your hardware synths:

1. Connect the MIDI IN of your hardware synths to a DIN MIDI OUTPUT on the MRCC
   
2. for each synth, you need to create a route in the MRCC from a PC INPUT to the DIN MIDI OUTPUTS so that Live can send MIDI to those synths
   
3. in Ableton, activate "Track" for the MIDI outs of the MRCC that are now connected to a synth, so that Live can send MIDI to those ports.
   
4. setup tour tracks in Live to send midi data on the correct channels
   

Maybe you want to take a look at the Cheatsheet I wrote for the MRCC, sometimes a second perspective can make things click.

After everything is working, save your configuration as preset in the MRCC, and consider creating a template in Live that set up the way you like it.