Hi Mike,
You’ll need to connect the Motif-Rack ES to your setup for both MIDI and audio communication.

We are not sure how many USB ports you have available on your computer, or how you MIDI keyboard controller connects for MIDI.
And without that information we could give you an answer but not be sure it would work for you.

But let’s assume you only have 1 USB port available and that your MIDI keyboard has actual MIDI jacks on the back.

Connect the 5-pin MIDI Out of the MIDI keyboard controller to the MIDI IN of the Motif-Rack ES.
Connect the Motif-Rack ES to your computer via a USB cable.
Download and install the Yamaha USB-MIDI Driver for your computer type and operating system: here
This driver will allow the Motif-Rack ES communicate with the computer for MIDI.
It will also allow the MIDI controller to communicate with the computer by sending messages *through* the Rack ES to the computer... in the computer you can reroute the MIDI messages to trigger the Motif-Rack ES via a MIDI Track in your software.

The computer will see the Controller on the so called THRU PORT... in the Rack ES you will find the parameter setting for this THRU PORT (example, Port 4)
This means in order to play your controller and have the Rack ES sound, you must create a MIDI Track that takes input from the keyboard (using the Thru Port number you set in the Rack ES), and reroutes it back Out via MIDI on “Motif-R ES-1” Port 1

Set the Motif-Rack ES so MIDI IN/OUT = USB

Connect the audio Outputs of the Motif-Rack ES to two channels of your audio interface.

Thank You very much for your reply.
I am sorry that I havent given you more information about my hardware. I have now somehow managed to connect everything, and my PC recognizes the Motif (It is recognized as a Motif ES Rack, and I have set the MIDI IN/OUT=USB). However, I still dont get the sound from the Motif ES Rack, even though it triggers the light of the VOICE knob when I press my keyboard. I have a PC with 6 USBs, a MIDI keyboard with a USB and a MIDI OUT, the AKAI EIE PRO audio interface, two monitors and the Motif Rack. These are the connections: Keyboard to AI via USB (if I connect it to the Rack it remains unresponsive), Rack to AI via audio and Rack to PC via USB, Monitors to AI via audio, then AI to PC via USB, and finally AI to Rack via MIDI (out to in). So is the problem in the connections, or is the setup fine? Do I have to change something in the Rack settings or in my DAW software? The only thing that is missing is the sound.
Thank You very much for helping me.

Kind regards

Thanks, because seriously, no one could guess about all of that.

Sorry but some of what you wrote makes no sense, and some is redundant.
We’ll take it a step at a time.

The “MIDI Keyboard” we assume makes no sound. We assume you are able to play on its keys and receive the MIDI messages in your DAW software.
In order to trigger the Motif-Rack ES, you must set the MIDI Out of an active MIDI Track to the Port and channel you want to sound.

If the Motif-Rack ES is in Voice Mode it will only receive on one MIDI Channel... most often the Rack ES is used in MULTI mode where it is 16 Part Multi-timbral. If you are connecting the Rack ES to the Computer via USB, (MIDI IN/OUT = USB) then you need to use the Yamaha USB-MIDI Driver and address it on “Yamaha Motif-R ES-1” Port 1

Only when you select a MIDI Track in your DAW that takes the Keybd IN and routes the OUT to the Rack ES) will the MIDI connection be complete from the Keyboard to the Rack ES.

If you see the light blinking on the Rack ES when you trigger keys you have a successful MIDI connection.

Sound is a separate problem. Take a pair of headphones and plug them into the Phones jack on the Rack ES. If you hear no sound the problem is MIDI channel related... if you do hear sound, then your issue is your audio connection between the Rack ES and your Audio Interface. Make sure your Audio Interface is receiving audio (peak indicators). Does it allow “direct monitoring”? if so activate that so audio can get to your speakers.

Thank you very much for this information. I have now successfully installed everything. The Rack now produces its sounds. I had a problem with the wrong audio connection as I put it in the wrong jack on the Audio Interface.

Thank you for your help