In single stack mode, I can make out everything that the DS shows, just brighter, with less contrast (if that makes any sense). It is like the features are more pronounced in DS mode, but all features still visible in single stack. (maybe a small prom or filament visible in DS mode only).
As stated above, sometimes I have to turn the DS stack a bit to get the best view and no 2 days ever seem the same without adjusting something with the etalon.
I usually let the single stack warm up at least for 30 minutes before I throw the DS on. I always adjust best view with single, add DS etalon, wait another 15 min, and start making minor adjustments with it ( minor tilt adj/etalon turn.) I am more of a surface detail person, so I usually am adjusting the proms out of it to get those nice surface features.