As soon as I boot up SX3.1.1, I always go straight to Devices>Device Setup>Virus USB ASIO Driver>Control Panel>ASIO and change Application Priority to another setting (doesn't matter which one, as SX3 overrides any changes to this parameter), and then click Apply.
After performing this little 'nudge' the audio works flawlessly for me.
Also, be sure to read
this article on PCI latency timings and their possible effect on audio.