You just need the plastic joiner on the center rail in order to run 2 loops separately.
The ground should be common between the 2 loops anyways via the TIU, so just leave the outer rails with standard joiners.
Whether you use the variable or fixed channels depends on what transformer you're using. With the Z-bricks, you'll want to use the variable channel to run conventional with the remote. With a Z4000, you can use a fixed channel and run conventional off the handle, or use the variable channel and run it with the remote.
