Ok, I'll simplify this a bit.
The "eX" models have the eX expansion installed in them. The eX expansion provides a third Level port, additional L Port (L5-6), Redox Sensor, and Conductivity Sensor. Not all packages come with the probes for these sensors, but they are available to the unit if you have the electrodes with your package or purchased them seperately. This expansion is the same for the II and the III.
The differences between the Profilux 2 and 3 base units are pretty extensive.
Profilux 3 has the following improvements over the 2:
- Integrated USB and LAN interfaces
- Integrated Web Server
- Dimmable LCD display
- 32 Programmable Logic Gates (instead of 8)
- 32 Illumination Channels (instead of 8)
- 32 Timers (instead of 12)
- PAB Bus Interface
- Significantly more expansion possibilities via Expansion Box
and much more...