Normally for add new extended subrack on OSN 3500, we select this option in U2000 equipment: NE panel, Display/Hide Extended Slot. After we see 2 new options: Extended Shelf y Extended Slot. Automatically U2000 should show in Extended Shelf the boards installed in extended subrack, but in this case that did not happen.
For U2000 recognize boards of extended subrack follow the next steps:
Check physical connections between EXA and EXB ports of XCE and XCSB boards and EXT ports of AUX boards.
If after to check connections U2000 dont recognize boards, click right in slot 59 and 60 and add XCE boards.
So U2000 shows you the boards installed in green color, add them.
Always you must to check first physical connections.