I used to use a tc 2290 to switch chs on a mkIII
worked fine .
for the 2290 though you have to make up " special " cables
that use the tip & ring of a " stereo / tip ring sleeve type
1/4 " plug on the t.c. side to normal tip & sleeve on the amp side
sleeve unconnected on the t.c. side , because it operated
as a fx loop as well .
check if this is the case for your situation