And/or ALL or any combination of bus A, B, C and D in separate amounts? I've had a look at the PGA4311 data sheet and your doc, and I still can't figure out if a true 4x4 mix is possible on one board. I can see 1 into 4, or 4 into 1, but I can't see how 4 into 4 works with only 4 volume controls. Wouldn't that require 16 volume levels in a matrix configuration? Please excuse the extreme dimness of the question.