Doepfer

I am aware that it likely is an abused subject but sincerely wasn't able to find the answer in the mailing list database. 

For room availability in the rack, I have to choose between one of the two. The most frequent use would be for audio (to mix multiplied signals and then send the output to stomp boxes via A-138d) though it might be adopted to mix control voltages sometimes.

As far as I can see, the “a” might be also used for audio mixing... didn't get if the “b” would work with voltages as well.

In other words, which is the more versatile?

Best, 
Diego