It varies from set up to set up how well you will get away with it,
If the laptop is plugged into the mains you will quite often get a lot of noise through powered speakers.
Unplugging the adapter from the laptop should make the noise go away if your cable is built correctly, but this is probably not practical for long periods of time.
However, those speakers say they have low noise - line level input, so you may get away with it...
I would suggest something like the Peavey USB-P (this is only 16-bit) as this will eliminate any noise from ground loops.