Asset purchases differ to DMOs in that the RBA is purchasing CGS with a 5-10 year maturity date in the secondary market, rather than short-term bonds in the overnight cash market. As a result, when there is more demand for the CGS, the price obviously goes up thence lowers the yield. So, instead of just lowering borrowing costs in the short-term (which is done through the adjustment of the cash rate), long-term borrowing costs are also low, allowing the government to run a large deficit with little servicing costs. That's the main difference between DMO and QE.
