Does anyone have any experience or knowledge of how Sonar manages DSD or DSF audio format files in a project - (2.8 MHz @ 1-bit or 5.6 MHz @ 1-bit).  I can see that Sonar will import these formats, but does it down-sample or reformat them first for playback?
 
Also, if you have practical experience in this area, do these files put a heavier strain on Sonar and if so, is it significant?

AFAIK, the format is only used for import/export. Inside SONAR itself it is working in PCM format.

All the math/calculations are in PCM format so yes, it has been decimated/down-sampled/reformatted. Sonar (and all other DAWs) do everything in PCM format. It is much more CPU efficient than doing it all in DSD. Ever wonder why DSD SNR is so high yet it has only 1 bit of resolution? All the noise is frequency-shaped to be above the audible range. It would create havoc with non-linear VSTs such as distortion/compressors which also generate high frequency content (which is why the best ones have their own internal over-sampling). All that high frequency noise needs to be filtered out first, which is what decimation/down-sampling does.

Ah, got it.  Thanks to you both.  I've done quite a bit of reading since my initial post and have a much better grasp on things now.  Cheers.