We hold all Australian assets under a custodial structure which are registered under IBKR's name at one omnibus account with our custodian, BNP Australia. Hence, stock is held on CHESS under the one HIN but underlying clients do not have a unique HIN for themselves.
If you are looking to transfer ASX shares into IBKR, please see: How do I submit an inbound position transfer from a financial institution located in Australia?