there is still a small bug in the gui with multi io:
my efx starts out with 1 input and 1 output. you can add tracks to get more inputs and outputs. the problem:
if you connect it up while there is 1 in and 1 output, you get the "old style" connection, with no plugs.
if you then add tracks to get more inputs / output pairs, you have to disconnect and reconnect to get the connection plugs for choosing the channels.
imho it should automatically switch the connection from a stereo to a multi-io-with-channel-plugs one if the number of inputs or outputs increases beyond 1.
or just always use the plugs...