An ED80 will piggyback just fine on a wedge mounted LX200GPS. Set your maximum slew rate back a few due to the increased mass that you are swinging around, to make things easier on your motors at the start of the slew.
I had an ED80 on a 10" LX200GPS using the Losmandy D style dovetail plate and guide rings, and a 2D counterweight system. It was quite stable in that configuration. Some shots for you to get and idea of how it was set up are
here.
Regards,
Eric