I'm one of those people that only updates every 3 years or so....
Using Nuendo 3 with updated Driver and Flash update on my FF800 on a PC running Windows XP

I have been using the Monitoring on the Fireface Mixer.
Was just checking the Direct Monitoring control to find that it doesn't work if you are using the Control Room function of Nuendo and have your Stereo Output Device Disabled.

Is this working in the current versions of Cubase or Nuendo?
Does it also work with the Studio Sends?
I use Multiple Headphone mixes

Thanks!
John