Both the A and B versions will work for both audio and control voltage uses, the only difference will be in how the knobs “feel” when you turn them. The A has Audio Taper pots which make audio sound louder in a more familiar way as you turn the pots, the Linear Taper pots in the B versions will not get louder in the same way, with the same turning distances for instance, but will still mix audio signals. If you mix by ear and not knob positions, there won’t be any difference between them. The A version is not Audio Coupled (having caps in the audio line to stop DC), at least mine don’t and I don’t even know which ones I’m using when I use them.

Oh, and they both have the normalized DC voltage on input #1, allowing a DC offset voltage to be added to the mix if #1 does not have a cable plugged into it. At least the ones made after 2004 anyway.
-James
James Husted, Designer, Synthwerks LLC • www.synthwerks.com • james@... • info@...