Go to Options -> Audio -> Advanced, and there is now a pull-down menu which allows selection of ASIO, WDM, MME 16-bit and MME 32-bit. You will need to restart Sonar for the new selection to kick in.

Also, another note, in Options - Audio - Drivers, since the ASIO protocol will only utilize one card type at a time, if you have multiple options for ASIO, you will need to completely de-select one card's inputs and outputs before the other options become available (they are greyed out).