SONAR does not make any use of audio drivers to render audio either on fast or real-time bounce - that's all happening "in the box". But it does use the same buffer size as your ASIO setting by default to process the data, unless you've altered BounceBufSizeMsec=0 in AUD.INI, which allows you to specify a fixed buffer size for bouncing regardless of the ASIO buffer setting.
 
If this setting has not been altered, I would recommend trying a fast bounce with a ASIO buffer set at a more typical 256-512 samples or setting BounceBufSizeMsec to an equivalent value from 6-12 msec, and see if that makes a difference.
 
In my experience, weird things can happen with extremely high or low buffers (say over 50ms or under 2ms).
 
Beyond, I think I'd have to see a sample project to try to reproduce or analyze the problem. Notwithstanding that some plugins produce different output from one rendering to the next, bounced audio should not differ from real-time playback at all.