Fixed Submix and Return tracks?

After not touching my MPC One for a while, I took it back out and am trying the MPC3 Beta. Something I can't understand (and I don't think this is new with v3) - is there a fixed set of 8 submix and 8 return tracks? Or if not, how can I add or delete them?

Just curious, and I don't see anything in the documentation for MPC2 or MPC 3...

They are fixed