HI dazza
RC's parallel interface can be configured to control up to 10 lanes (ie, you can assign lane numbers to 10 pins in the parallel port interface screen). In case you are interested, I've had RC control up to 6 sensors on my 3 lane track - 3 for lap counting and 3 for pits.
RC's phidget interface can be assigned to as many digital inputs you have on your phidget board. I am currently using a phidget 8/8/8 board on my 3 lane track to receive input from 3 lap sensors and 3 pit sensors. With this board you could easily control an 8 lane track (ie, assign all 8 digital inputs to read lap sensors). Also, phidget make a 0/16/16 board which has 16 digital inputs and 16 digital outputs so you could control a 16 lane track with that board.
RC's arduino interface shows it can control up to 8 lanes but currently it is limited to the arduino sketch code bundled with the 1.7.1.13 beta version which programs the arduino uno to control up to a 4 lane track. The arduino uno has 14 digital inputs/outputs so if the sketch code existed it could control more lanes.
Cheers
John