I don't own the latest version of Mixbus, so I can't try this myself, but I wonder if it would be possible to mix in Mixbus like we do in Sonar using the VS-700 and its typical layout
 
according to Harrison videos it should be possible to set it up in Mixbus (there was even a "v-studio 20" template showing in one of the videos, so is there also a V-700???)
 
 

no one replied, so no one has tried
 
anyway, will give it a try myself in the coming weeks - just went for the update to the latest version. videos on Mackie capabilities look promising.
 
 

this turns into a monologue ... let's call it my blog ;-)
 
First problem: instant crash of Mixbus when using it with ASIO VS700 despite working OK with other ASIO devices.
 
Harrison support was quick and pointed to the "buffered audio" option below which seemed to have solved it ...
 
The Roland drivers have been troublesome for us; so troublesome that we added an option specifically to make them work better. Please try clicking the "buffered audio" checkbox in the Audio Setup dialog, and tell me if that allows the Roland device to work better.

You might also try using a different device ( such as choosing PortAudio, MME, {internal soundcard in&out } to verify whether Mixbus is crashing on -any- device, or if it is associated with the Roland device.

OK - 2 more important facts (regarding Mixbus 3.3) from recent ventures:

1. 'clicking the "buffered audio" checkbox in the Audio Setup dialog' is very important and needs to be done every time before you start Mixbus. Apparently it is not saved and left me wondering why I only manage to start Mixbus 1 out of 10 desperate times, then stumbled across a post in another forum saying that this is (although indicated as saved by LED display) apparently not saved properly. Thus this control needs to be cycled any time Mixbus v3.3 is started. Since I do this it comes up everytime and exits fine, releasing the audio driver.
2. The VS-700 in Mackie control is somewhat supported i.e. you get transport, fader control, pan, mute, solo, banks up/down. I have not yet figured out how to access the EQ section (will try some MIDI remapping in the next days/weeks) but realized it works fine when done via a cheap BCF2000, so I reckon eventually this may also work for the VS-700 surface.