i have a setup where i will switch between an asio external soundcard and my laptop on-board audio (conexant with realtek drivers) running in wasapi mode (win 7 x64) try this, i've found it to be very stable when switching between the two audio devices...


in preferences/audio/configuration file change the following
 
usewdmdmaforwasapi to false  ksuseinputevent to false  allowofflinerendermixthreads to false  threadschedulingmodel to 2  minimizedriverstatechanges to 3  extrapluginbuffers to 32  dropoutmsec to 750