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The Losmandy G11s digital drive uses stepper motors and the unit has an HC/CCD port meaning you connect the handcontroller to this and ST4 autoguide by use of a shoestring GPSUB.
This allows autoguider (and hand controller) signals to be fed to the system. This system is essentially a "push to" meaning you align your mount setting circles and push the mount to the desired object. The main reason is that the stepper drives are very slow is "slew rate" to be of any use. Alternately many users of this system use external digital setting circles and "push to" (like the JMI NGC-MAX). This is more accurate as the art of using setting circles is almost lost!
Of course this can be a bit laborious in finding dim objects but many users enjoy this part.
The Gemini 2 is a servo system that employs DC servo motors (with inbuilt encoders) and electronics system that has inbuilt object catalogues etc. You can command the system to go to an object and it will slew to it rapidly as the servo motors can run at much faster rates (compared to the Digital drive). Thus the Gemini 2 is a "goto" system meaning you ask it and it will go to the object commanded.
This makes it easy to find dim DSOs etc (if aligned well). The Gemini 2 can also be controlled by ASCOM and other planetarium programs which makes it versatile.
There no great advantages of a DC servo over a stepper system. But in this case, Losmandy has kept the digital drive system as an entry level and the Gemini 2 for those who like goto systems.
They both track in RA equally as well its just the Gemini 2 has much more functionality and connectivity, such as LAN, USB, RS232 etc. Thus this is more suited for astrophotography. Well IMHO.
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