The lxd75 was not meant to use autoguiding, but you can. There is a module called a apm 909, which is made for the meade lx90 that plugs into the aux socket and provides an st4 (pretty much the autoguiding standard) input for autoguiding and also a control for motorised focuser and illuminated reticle control.
You will need to reflash your autostar controller with a version modified by Dick Weasner from (
www.weasner.com) that accepts autoguiding commands for the LXD75, as the meade version does not.
There is a guy in the states called Gene that makes a 909 clone. I have bought 2 from him and they work great. His site is
http://home.comcast.net/~lynol1000/a..._909_clone.htm
If you want to guide from the dsi you will also need a Shoestring Gpusb
The plug at the bottom of your hand paddle is for a autostar serial cable to your computer for driving your mount with a planetarium program and for reflashing.
Hope that helps
Brett