Okay, you want to make sure the Audio Output of the Motif XF arrives at the inputs in Cubase.
In Cubase, go to DEVICES > VST CONNECTIONS > Select the INPUTS tab

Here is where you connect the Audio coming from the XF to Inputs that your Audio Tracks will use.

As you can see below there is no YAMAHA Steinberg FW to choose. I think there must be a problem with the driver.
As I said before the firewire connection between the MotifXF and the MacBook is ok. Just Cubase is picky when trying to find the FW.
It actually does, but just every 10th time when starting it again. Sorry for maybe being unclear before!
Should I install the driver a second time?

As you can see below there is no YAMAHA Steinberg FW to choose. I think there must be a problem with the driver.
As I said before the firewire connection between the MotifXF and the MacBook is ok. Just Cubase is picky when trying to find the FW.
It actually does, but just every 10th time when starting it again. Sorry for maybe being unclear before!
Should I install the driver a second time?

And sorry for my answer being doubled again. 🙁 This "upload error message" really should be reprogrammed on this site!
You can´t really see that your answer already was posted until the REPLY button is pressed sucessfully. Sorry again...

As you can see below there is no YAMAHA Steinberg FW to choose. I think there must be a problem with the driver.
As I said before the firewire connection between the MotifXF and the MacBook is ok. Just Cubase is picky when trying to find the FW.
It actually does, but just every 10th time when starting it again. Sorry for maybe being unclear before!
Should I install the driver a second time?

No. Let's first verify that it is installed. There are no known issues with this driver.

Let's work backwards so we don't unnecessarily do again we don't need to...

In Cubase, go to DEVICES > DEVICE SETUP > VST AUDIO SYSTEM
Here is where you select the Audio Interface... switch it from the one you have selected to the Motif XF's "Yamaha Steinberg FW"

Let us know.

Make sure your Motif XF is powered on, completely, when you launch Cubase. It is during the launch that Cubase surveys connected items. You can actually see it find and negotiate the connection. If it is not there when you launch Cubase, it will not select it. However, if it is there it should find it every time!

In the meanwhile I installed the newest version of the driver directly from the Steinberg site and now it finally seems to work.
Thank you for the great support. I really do hope that this is solved permanently now.
Now I also finally can see all the activated ports coming In and out. This wasn´t before.

THANK YOU!!!

It can't work without the driver! 🙂