set the sample rate to 30MHz or the maximum that usb2.0 allows

Sample rate can only be set to 75MSPS, 7.5MSPS,750ksps, 75ksps, etc ... 

Oversampling ratio can be set to an integer value. Oversampling ratio cotnrols a decimator between the converter and the buffer.

There is no way to get from 75MSPS to 30MSPS .. closest would be 32.5MSPS by setting oversamping ratio to 2

Thanks