Cubase 7 changing MR816csx audio path

My system configuration is as follows:
MAC-pro Mavericks 10.9.1
Cubase 7.5
Yamaha Motif XF8
Yamaha Tyros4
Steinberg MR816CSX
My Firewire software version is V1.7.3, My IEEE1394 software version is V1.08, MR816CSX is main version V1.10 and IEEE 1394 version V1.02.
The following I am trying to achieve:
The audio output from the Motif XF8 is connected to the MR816CSX inputs 5 and 6.
The audio output from the Tyros4 is connected to the MR816CSX input 7 and 8.
In Cubase 7.5 I have a midi project. I am using the Motif XF8 synthesizer through IEEE 1394 interface. I have added an audio track to the midi project
The audio output from Cubase 7.5 needs to be connected to MR816csx through IEEE 1394 connection to either inputs 1~2, or 3~4.
AS long as Cubase 7.5 is not active, I hear the Audio from both units through MR816CSX headphone output 1
When I start Cubase 7.5, the audio from the Tyros4 is no longer heard from my MR816CSX headphone output
Somehow Cubase 7 disables that audio path.
How can I configure Cubase 7.5 to achieve the above specified achievement?

Thanks for your help

Mr816csx uses an “extension” to “integrate” with Cubase. Personally, I prefer to use the MR816 editor/mixer app to monitor independently of Cubase so I uninstalled the MR816 extension. This allows you to do all your routing/monitoring outside of Cubase. Also, I would hook up ONLY the MR816 to the computer via firewire.

Hi Beatpete,
Thanks for your help. uninstalling the MR816 extension gave me the configuration I wanted to achieve. I did need to keep my Motif XF8 and MR816 connected since I use the Motif XF8 synthesizer.