Gday Patti
The ETX and LX90 use "roughly" the same firmware, but different hardware.
The ETXs (forks) are the smaller sizes ( up to 125mm) and have basic hardware mounts
The LX90s (forks) are 8",10",12" and have better mechanicals.
There are also LX GEMS, but i dont know their sizes.
The LX200GPS's use different firmware/handboxes with much more functionalityand much more robust mounts. Much more expensive tho.
Notwithstanding that, many people track stuff quite happily using ETXs.
If it has an Autostar controller vs just an EC controller, you can add satellite data and it it can track.
If you go to Weasners site
http://www.weasner.com/etx/autostar_info.html
you can get heaps of Autostar specific tips on what each model can and cant do.
Andrew