Nothign wrong with the idea, but the dynamic range and power requirements for film are a lot more than for music.
The biggest issue you would face is the disparity between your mains and everything else when listening to movies. You could alleviate this somewhat by setting the L/R speakers to "small" and routing all bass through a sub.
The biggest issue you would face is the disparity between your mains and everything else when listening to movies. You could alleviate this somewhat by setting the L/R speakers to "small" and routing all bass through a sub.