For background in streaming with the UD driver, see the pseudocode in Section 4.3.7 of the U6 User's Guide:
The SimpleStream example for VB.net does 2 channels at 1000 scans/second by default. The example uses wait mode NONE, and reads stream data in a Timer event that happens every 500ms. Does this work?
Looks to me like all you need to do to scan at 600 scans/second is change scanRate to 600. Does that work?
Next, you want to process that data down to 60 scans/second by averaging each 10 scans. You could do that using wait mode NONE but it will be a little tricky since you don't know the exact number of scans you will get each time. It would be easier if you used the SLEEP wait mode.
With the SLEEP wait mode, you don't want a delay in the read loop as the read call is blocking. The other change is that you want to set NUM_SCANS_REQUESTED to the exact number you want ... say 600 to get 600 scans per read which will take about 1 second each time.