The ASM308EXT allows the ASM308 to be converted in to a 4-in/n-out CV Matrix Mixer.
For a 4x4 CV Matrix Mixer you could use the CGS733.

Each ASM308EXT is supplied with a '3x Output -Stage' caable. If the ASM308EXT(s) are purchased separately from the ASM308 then the 2nd cable is not required

Build Guide