[MrFlippant]

Most of what has been written above is accurate, but it IS possible to use oXigen on a stock Carrera track, without replacing all of the lane change electronics. You can even have the Carrera Digital control unit count laps. As such, all you'd really need is the controller(s) and car chip(s) to give it a try. I think I might have seen similar claims from Scorpius, but I can't speak to that with confidence.

Of course, neither will have the full feature set each system offers until you replace the lane change electronics for those dedicated to that system, but it can be made to work. 

To go "full oXigen" you'd need to glue some magnets under the track in the right places for the pit entry/exit and the finish line, replace the LC electronics, and get the USB dongle for your computer to run the race management program.

Both the oXigen and Scorpius controllers are considerably more advanced than other available controllers for the off-the-shelf digital systems, but each have strengths and weaknesses. While Scorpius controllers have lots of buttons and knobs, and a really nice LCD display, navigating the display and making adjustments to the throttle curve and other settings can be quite tedius. The slot.it controller has a simpler 7seg LED display, but complete throttle curve control is a simple tweak of a knob or two away. In spite of plenty of feedback and suggestions/request from users, the Scorpius interface has remained unchanged since it's initial public release, with no indication of future improvement. The ergonomics of the two are also quite different, and one may suit you more than the other on that grounds alone.