A multiple I/O sound board or a mixing desk?

Hello,

I need to connect my hardware synthesizers to my computer and I wonder if I should buy one/two MOTU 24i/o sound board(s) or a mixing desk such as an Allen & Heath ZED-436.

I use a number of VSTIs on Cubase, and I also use external synths for inhouse psychedelic goa trance performance, not live.

I'm puzzled. I'm not sure how to route audio outputs (from soft and hard synths):

» What about using both MOTU sound board and mixing desk? That way, the VSTI outputs could come out from the sound board to the mixing desk and I could control them on the mixing desk.

» Or is it better practive controlling all audio outputs on Cubase virtual mixer, even the hardware synth audio outputs within the Cubase mixer?

» What about controlling VSTI audio outputs withing Cubase virtual mixer, and controlling hardware synths outputs on a physical mixing desk? Any suggestion?
Thanks! kfhkh