Theoretically you can change to a weber sensor, but you will have to change the plug and the pin config, but it wont make a blind bit of difference to the original sensor
These displays arent really worth the bother, its very small, the air temp sensor will need tapping into the main 'V6' pipe, but the sensor they use is a slow update thermistor, which isnt very accurate for inlet temps, the 'water injection controller' is just a relay than can be set to trigger at a certain boost pressure/temp, but you still need to buy a water injection system, and the lambda system (if you had a sensor) is narrowband display only, so hardly any usable, visible range..
And yes, you cant upgrade the standard 2 bar to a 3 bar on the original ecu. Basically all map (1,2 and 3 bar) sensors kick out a voltage from 0 to 5v depending on pressure (0 being max vacuum and 5v being max pressure of that particular sensor)..so if you stuck a 3 bar on a 2 bar system it would think 14psi for instance, was 8 psi, and therefore the fueling and ignition timing would be completely out. It would need a mappable ecu to therefore be completely recalibrated.