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You have to separate two things here:
1) Async compute feature in the application
2) Async compute feature in the driver
If you deselect async in Time Spy, then it will submit all tasks to a single queue, therefore the driver won't be able to schedule the tasks in parallel, even if it has that ability.
However, even if Time Spy creates multiple queues, the driver could still put them into a single queue internally (effectively disabling it), if the driver developer thinks this is more efficient than using multiple queues. That is what nVidia chose for Maxwell v2, but not for Pascal.