Hey, Phil. I've not personally tried the DiMarzio Black Angel blend system. I've heard nothing but good things about the Black Angel. One of our wonderful artists, Mike Dawes actually helped in the development of the Black Angel.
You should have zero issue blending the magnetic soundhole pickup with the piezo.
The only blend systems that can provide trouble are microphone blend types.
Phil Eisenhower
Has anyone tried the Dimarzio Black Angel blend?