The ion expansion, with the 9 additional parallel ports, is a one time setup.  You connect your pads and cymbals to the ion expansion, then patch in your DM5 with short patch cables from the 9 parallel ports.  You can play with or without the dm5 brain,  or play them together.  No need to ever swap cables.  No Y cables needed.  The j5's automatically come with the additional ports.  They are optional for the ion expansion if your not using an external drum brain.