By law the official address for the service of legal documents for a company is the address registered with ASIC.  A statutory demand sent to that address will be deemed to have been served and if the defendant does not respond within 21 days in the manner required by the Corporations Act (Section 459E) a legal presumption of insolvency applies.  In fact in order to serve a statutory demand you must provide proof of having conducted an ASIC search to establish the creditor's registered office.  All of this is laid down by statute - it's not negotiable.  You lawyers can absolutely go to court and get a default judgement if there is no response to a statutory demand within the period required by statute.  They can even apply for the company to be wound up in insolvency on the basis of non-compliance with a statutory demand if you're willing to spend the money to go that route.

I simply don't believe that your lawyers are too incompetent to know this - it's business law 101 stuff.