Is it possible to switch from tuner A to tuner B to zap channels on b or visa versa ? I can't find anything about that on the manual.
Switch between tuners is automatically when you made a recording.
If you have two different LNBs connected to your tuners, the switch is automatically done when you try to tune the satellite configured into other tuner.
For example:
Tuner A: Astra 28.2E
Tuner B: HB 13E
When you try to tune a channel on HB13, the box uses automatically the tuner B and vice versa for Astra 28.2.