Yes what Wilkie Said. All you are doing is putting the Stage 3 circuit (always on) on a switch to either be in the Audio Path or removed. Again the Buff N Blend was designed to be used mostly with a single “main circuit” so it can all fit in a small enclosure.
We us the Paramix (link above) for a larger multi-purpose application as you are demonstrating above. Yours will still work however as Wilkie1 has pointed out.