If you have two monitors (I do).
Open Vixen, it will start maximized to one monitor
Click the middle button, not minimize of maximize
Grab the lower right corner of the window and stretch it to fit across both monitors.
Open a sequence but only make that window the size of one monitor. When you play the sequence just drag the preview window to the second monitor.
When I am trying to adapt one of my old sequences or one that I downloaded I put my new sequence in the left half of the window (left monitor) and the old/dl one in the right half of the window (on the right monitor). You can then copy and paste between the two loaded sequences.
Vixen does not support two independent windows, only windows within the main window.
Anyway works great.