It looks like the page listing downloads is down, but direct links to the downloads still work. I believe that this is the file that you're looking for:
It is not a protocol limitation. It is a sensor limitation. There is a microcontroller on the LEGO EV3 Ultrasonic sensor that cannot be updated so there is no way to measure more than that. So to measure more than 255cm, a 3rd party sensor is needed, e.g. https://mindsensors.com.
It depends on what you're doing, but for this purpose the Mindsensors motor multliplexer is the device you are looking for - not the port splitter.
A multiplexer (in this context) allows you to independently control/communicate with multiple devices over a single port, one at a time. A motor multiplexer will also need an external power source because a ...
This isn't exactly sending direct commands to your robot, but LEGO Education recently released a python stack for the EV3 brick.
I haven't tried it; but as I understand it, it's an alternative firmware which should allow you to have python scripts running natively on your EV3 brick, allowing for full autonomous robots programmed in python.
Since I'm no software engineer my solution would be to retrofit the insides with known compatible hardware. Cheating? Maybe... but it isn't like the original hardware inside was actually Lego to begin with. The mention of potentially using "compatible software" would seem to be already stepping out of bounds with "only official Lego parts", since it didn't ...