Electrical – How does a level shifter shift the DC level of a multi-stage amplifier output to the ground (or zero)

Use Power MOSFETs with very low Rdson. Look into an N-channel as well, to reduce Rdson. Don't forget to manage heat dissipation. Even at 90% efficient, you still need to dissipate 80W! Since your microcontroller probably can't drive the FET quickly enough, you probably need a preamp/level shifter stage as well.

See http://www.onsemi.com/PowerSolutions/product.do?id=NVD5890NL as an example.

You don't mention your application, but if you are trying to build an audio amplifer, open loop Class D amplifiers are limited in their THD.

The first buffer outputs a clipped signal between 0.5 - 10 V losing some data by clipping it, which is shifted down to 0 - 9.5 V, still being clipped. The second buffer doesn't modify this in anyway, so to answer your question: the output would still be clipped.

Remember, voltages are only potential difference. Amplifiers reference their input signals to their ground and power supplies, so in order to prevent clipping, you could shift the first buffer's ground and voltage supply up by 0.5 V. I dont see any use for that though..

Edit: I assume you have 10.5V < power supply available for your lever shifter for them to work. Depending what are the power supplies for the buffer amplifiers, they just might pass the 10.5 V without clipping the signals even though datasheet says otherwise.