The Miele S163 has been discontinued, the S194 is the current Miele stick vacuum on the market. Here are some difference between them:

Miele S194 vs S163
images from manufacturer

Optional Motorized Attachment:
The Miele S194 has a socket for motorized floor tool whereas the S163 does not have this socket.

Wand:
The wand of Miele S163 is non-telescopic while the wand type of S194 is telesopic that allows it to fit your height.

Color:
Miele S163 is Black while the S194 is Red.

Operating Radius:
Miele S163 has a 26 ft operating radius while the S194 has a 28 ft cleaning radius that provides longer reach.

Floor Tool:
Miele S163 comes with the SBD 245 Combination Rug / Smooth Floor Tool for cleaning smooth flooring and low pile rugs/carpeting
while the S194 comes with the new SBD 470-3 FiberTeQ Combo Floor Tool.

If you know more difference between Miele S194 and S163, please share below.