With the Apex you get the variable speed controls and an extra probe connector that you can use for pH or ORP.
With the Lite you do not get those two things, you get 1 probe connector and then a bunch of the other standard ports, serial port I/O port etc.
Essentially the APEX comes with a Probe Module built in. an ORP probe module would come with the BNC connector and controls for variable speed ports.
I own the APEX and I would recommend just getting the full model.
Apex is on sale right now at Oceanic Corals for 499, so get J&L to match that price.
http://www.oceaniccorals.com/store/i...&productId=356