Hi Andy.
I don't have the Ioptron nowdays but I did put a document on all this on the NJIdea yahoo forum (above link) and the
Ioptron Yahoo forum.
The old NjIdea forum is not moderated anymore so is nothing but a spam fest but the documents would still be there. The Ioptron forum??? sorry I am not a member of them anymore.
Ioptron are selling
the interface on their website and have some instructions in a link on that page.
However to cut to the chase, just connect the Guide ST4 to the interface and the interface out plug to any of the HBX ports and it will work..oh..and you need to have the latest firmware and have the handset in the autoguide sub-menu for it to work.
Hope this helps! Good luck.