It won't be possible with the current firmware, the clock to the ADC is changed constantly after each capture (for triggering purposes). For the subsampling to work correctly, the clock to the ADC has to be fixed. However, this may change in a future update, so subsampling is a possibility.
Other inconviniences:
1) The analog bandwith is set at 2MHz, a 9MHz signal will be attenuated by a few dB./\r\n/2) Triggering on a 9MHz signal will be a little difficult for this system, so you will see some jitter when analyzing the signal in the time domain.
Let me know if you need more info.