Cam, I would think you should make the shelf a little deeper for these two reasons: 1) give yourself a bit more room for wiring esp if you are using Banana Plugs which will need more room and 2) you may decide to set the VP150 on it's angled side which will effectively increase it's width.

I'd suggest 9" or even a tad more for safety.

Half of communication is listening. You can't listen with your mouth.