Hi Tommy
Thanks for outlining this method, this is one of the ways I want to use Mixbus with X3.
However, I must be doing something wrong. I set up Mixbus as you suggest, but once I change focus to SONAR (to select a track) I get this message:

There are no options to reassign my TonePort (my soundcard) to SONAR after I close this message.
My TonePort has 2 Ins, but even if I set a track up to in advance of opening Mixbus to input from 3-4, I still get the same message.
I checked my Preferences in SONAR and I have "
Share Drivers with other Programs" checked.
No doubt I'm missing something incredibly daft, but I can't figure it out!
Hi Steve,
Try and start Mixbus first and Sonar second. I haven't had any issues at all with drivers. They just open up in both. Does Toneport have more than one IN pair and one OUT pair? For this to work you have to have a route out and in as well as main outs. I'm using patchbays to physically patch the I/Os.
I also set it up so I can go directly from Sonar to Mixbus using basically the same setup.
I inserted stereo tracks in Mixbus and set their inputs. Set my drum bus OUTS in Sonar to an OUT and patched that to the in selected in Mixbus. It worked perfectly. This is very handy. I can even patch out of Sonar into Mixbus and back into Sonar. This is crazy and changes my whole setup.
There are limitations for sure but I like the early returns.