DS1681+ has 2 pools. Want to move one pool to a different unit and expand the other pool in its place

So I have 4 SSD which is volume 2 and 2 HDD as volume 1. id like to move volume 1 to a ds220+ and use the 2 drive slots on the 1681 to expand the other pool with 2 more SSD. Now the OS and the config and apps are on volume 1, so how would I make this happen? can’t be as simple as taking the 2 HDD out and moving them to a DS220 because then the 1681 wouldn’t have configuration, right?