Miele S194 vs S168
images from manufacturer

The Miele S168 is an old model, it has been discontinued, and replaced by the S194. Here are some difference between them:

Filter:
The Miele S168 comes with the Active HEPA filter that can capture 99.97% of all particles down to 0.3 microns.
The Miele S194 comes with the Active Air Clean Filter that can capture 94% of particles as tiny as 0.3 microns.
The Miele S194 can also upgrade the filter to HEPA version.

Floor Tool:
Miele S168 comes with the SBD 245 Combination Rug / Smooth Floor Tool while the S194 comes with the new SBD 470-3 FiberTeQ Combo Floor Tool.

Color:
Miele S168 is in White while the S194 is in Red.

Cleaning Radius:
The S194 provides longer reach, it has a 28 ft cleaning radius while the Miele S168 offers 26 ft operating radius.

If you know more difference between Miele S168 and S194, please share below.