hmm...shouldn't be very complicated in theory, but i think practically
you'll need power to do it (and some sort of casing to house the
parts, obviously). switching between two signals in dependency of a
third on/off type signal could be done with a relay or possibly with
one/two transistors...but you'd need power for this. so you've got
1) cv 1
2) cv 2
3) 8/16 select
4) ground
5) +V
6) -V
...kind a thick cable :/

.....i think you'd be better of with modules and pre-patching them
with the normalling-switches in the sockets

l8a
d