Can I get faster than 33 ksamples/second for A/D on my Netduino Plus 2?
Apparently the Netduino Plus 2 uses the STM32F405RG microcontroller. Looking at the datasheet, you should be able to sample much faster than 33 kSa/s:


While slightly reduced performance is to be expected when using any abstraction layer (like the netduino libraries), 180 times slower sampling is not normal. Do you mind posting the code?  

By writing your own ADC code you should be able to take full advantage of the hardware, but there is a considerable drawback: the microcontroller is approaching SoC -level complexity, with the reference manual having 1731 pages, so the effort might not be always worthwile.